Showing papers in "Topics in Catalysis in 2016"

H2 Production via Ammonia Decomposition Using Non-Noble Metal Catalysts: A Review

Abstract: The wide-spread implementation of the so-called hydrogen economy is currently partially limited by an economically feasible way of storing hydrogen. In this context, ammonia has been commonly presented as a viable option for chemical storage due its high hydrogen content (17.6 wt%). However, its use as an energy carrier requires the development of catalytic systems capable of releasing hydrogen at adequate rates and conditions. At the moment, the most active catalytic systems for the decomposition of ammonia are based on ruthenium, however its cost and scarcity inhibit the wide scale use of these catalysts. This issue has triggered research on the development of alternative catalysts based on more sustainable systems using more readily available, non-noble metals mainly iron, cobalt and nickel as well as a series of transition metal carbides and nitrides and bimetallic systems, which are reviewed herein. There have been some promising cobalt- and nickel-based catalysts reported for the decomposition of ammonia but metal dispersion needs to be increased in order to become more attractive candidates. Conversely, there seems to be less scope for improvement of iron-based catalysts and metal carbides and nitrides. The area with the most potential for improvement is with bimetallic catalysts, particularly those consisting of cobalt and molybdenum.

Conceptual Process Design and Techno-Economic Assessment of Ex Situ Catalytic Fast Pyrolysis of Biomass: A Fixed Bed Reactor Implementation Scenario for Future Feasibility

Abstract: The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Ex situ catalytic fast pyrolysis of biomass is a promising route for the production of fungible liquid bio- fuels. There is significant ongoing research on the design and development of catalysts for this process. However, there are a limited number of studies investigating process configurations and their effects on biorefinery economics. Herein we present a conceptual process design with techno-economic assessment; it includes the production of upgraded bio-oil via fixed bed ex situ catalytic fast pyrol- ysis followed by final hydroprocessing to hydrocarbon fuel blendstocks. This study builds upon previous work using fluidized bed systems, as detailed in a recent design report led by the National Renewable Energy Laboratory (NREL/ TP-5100-62455); overall yields are assumed to be similar, and are based on enabling future feasibility. Assuming similar yields provides a basis for easy comparison and for studying the impacts of areas of focus in this study, namely, fixed bed reactor configurations and their catalyst development requirements, and the impacts of an inline hot gas filter. A comparison with the fluidized bed system shows that there is potential for higher capital costs and lower catalyst costs in the fixed bed system, leading to comparable overall costs. The key catalyst requirement is to enable the effective transformation of highly oxygenated biomass into hydrocarbons products with properties suit- able for blending into current fuels. Potential catalyst materials are discussed, along with their suitability for deoxygenation, hydrogenation and C-C coupling chem- istry. This chemistry is necessary during pyrolysis vapor upgrading for improved bio-oil quality, which enables efficient downstream hydroprocessing; C-C coupling helps increase the proportion of diesel/jet fuel range product. One potential benefit of fixed bed upgrading over fluidized bed upgrading is catalyst flexibility, providing greater control over chemistry and product composition. Since this study is based on future projections, the impacts of uncertainties in the underlying assumptions are quantified via sensitivity analysis. This analysis indicates that catalyst researchers should prioritize by: carbon efficiency(catalyst cost(catalyst lifetime, after initially testing for basic operational feasibility.

Exploring the Influence of the Nickel Oxide Species on the Kinetics of Hydrogen Electrode Reactions in Alkaline Media

Abstract: The influence of the oxidation of Ni electrodes on the kinetics of the hydrogen oxidation (HOR) and evolution reactions (HER) has been explored by combining an experimental cyclic voltammetry study, microkinetic modeling and X-ray photoelectron spectroscopic analysis. Almost 10 times enhancement of the activity of Ni in the HOR/HER has been observed after its oxidation under the contact with air at ambient conditions and assigned to the presence of NiO species on the surface of metallic Ni. The experimental cyclic voltammetry curves have been analyzed with the help of kinetic model in order to shed light on the mechanism of the HOR/HER for two types of Ni electrodes and its dependence on the presence of NiO on the surface of the electrode. The main features of the experimental current-potential curves can be reproduced with a kinetic model assuming that the free energy of the adsorbed hydrogen intermediate is increased and that the kinetics of the Volmer step is enhanced in the presence of nickel oxide species. The kinetic model provides evidence for the switching from the Heyrovsky–Volmer mechanism on metallic Ni to Tafel–Volmer mechanism on the activated electrode, where surface oxide species co-exist with metal Ni sites.

Stabilization of Softwood-Derived Pyrolysis Oils for Continuous Bio-oil Hydroprocessing

Abstract: The use of fast pyrolysis oil as a potential renewable liquid transportation fuel alternative to crude oil depends on successful catalytic upgrading to produce a refinery-ready product with oxygen content and qualities (i.e., specific functional group or compound content) compatible with the product’s proposed refinery insertion point. Similar to crude oil hydrotreating, catalytic upgrading of bio-oil requires high temperature and pressure. However, processing thermally unstable pyrolysis oil is not straightforward. For years, a two-temperature, downflow trickle bed reactor using sulfided catalysts was the state-of-the art for continuous operation. However, pressure excursion due to plug formation still occurred, typically at the high-temperature transition zone, and led to a process shutdown within 140 h. A plug typically consists of polymerized bio-oil and inorganic constituents that bind catalysts at specific portions preventing liquid and gas flow through the bed, resulting to a potential pressure incursion. Recently, two factors were found to enable continuous operation by preventing reactor shutdown due to plug formation: (1) a bio-oil pretreatment process prior to the two-temperature reactor, and (2) a robust commercial catalyst for the high temperature zone reactor. Here, we report the use and characterization of bio-oil that was pre-treated at 413 K and 8.4 MPa under flowing H2 (500 L H2/L bio-oil, 0.5 L bio-oil/L catalyst bed) to enable the long-term (cumulative 1440-h) bio-oil hydroprocessing.

Effect of Location and Distribution of Al Sites in ZSM-5 on the Formation of Cu-Oxo Clusters Active for Direct Conversion of Methane to Methanol

Abstract: A series of Cu/ZSM-5 materials were synthesized and tested for the selective oxidation of methane to methanol reaction in a three stage reaction. The efficiency of the catalysts is related to the ability of the zeolite framework to stabilize multinuclear Cu-oxo species, namely dicopper and tricopper oxo clusters. Spectroscopy characterization by EXAFS showed that the exchange with moderate Cu loadings led to preferential formation of trinuclear Cu complexes [Cu3(μ–O)3]2+ in HZSM-5. The concentration of Al pairs in ZSM-5 is found to limit the maximum concentration of multinuclear Cu-oxo species that can be formed. Above such maximum, inactive Cu species including Cu oxide nanoparticles are formed. Conversely, it was found that at low loadings the Cu speciation in Cu/ZSM-5 occurs as a mixture of Cu monomers and dimers. Furthermore, it was found that not only the structure of Cu-oxo clusters is relevant for the activation of methane, but also the local environment in which the cluster is embedded. Comparison of methane to Cu stoichiometries achieved for Cu/ZSM-5 and Cu/MOR systems containing the same type of active [Cu3(μ–O)3]2+ cluster shows that approximately 50 % of these clusters are inactive on ZSM-5. While MOR stabilizes the trinuclear clusters in highly constrained 8-MR side pockets, the possibility of ZSM-5 to stabilize part of these clusters in less constrained local environments might be the reason for a lower activity in methane oxidation.

On the Mechanism of CO and CO 2 Methanation Over Ni/CeO 2 Catalysts

Abstract: The reactions of the CO and CO2 methanation in the excess of hydrogen were studied over Ni/CeO2 and Ni(Cl)/CeO2 catalysts prepared from nitrate and chloride precursors, respectively. Macrokinetic parameters of the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts were determined. The nature of surface species during the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts was studied by the Fourier transform infrared spectroscopy in situ technique. It was shown that the CO methanation proceeds similar ways over both Ni/CeO2 and Ni(Cl)/CeO2 catalysts via CO and H2 chemisorption on the surface of Ni particles. The CO2 methanation over Ni/CeO2 catalyst proceeds via the CO2 adsorption on the ceria surface and stepwise hydrogenation to methane through hydrocarbonate and formate intermediates by the hydrogen spilled over from Ni particles. With the Ni(Cl)/CeO2 catalyst, this reaction pathway is locked due to the ceria surface blockage by chlorine, to inhibit the CO2 methanation and therefore provide a high efficiency of Ni(Cl)/CeO2 catalyst in preferential CO methanation in the presence of CO2.

Photocatalytic Activity of Mesoporous Graphitic Carbon Nitride (mpg-C3N4) Towards Organic Chromophores Under UV and VIS Light Illumination

Abstract: A template-assisted synthetic method including the thermal polycondensation of guanidine hydrochloride (GndCl) was utilized to synthesize highly-organized mesoporous graphitic carbon nitride (mpg-C3N4) photocatalysts. Comprehensive structural analysis of the mpg-C3N4 materials were performed by XPS, XRD, FT-IR, BET and solid-state NMR spectroscopy. Photocatalytic performance of the mpg-C3N4 materials was studied for the photodegradation of several dyes under visible and UV light illumination as a function of catalyst loading and the structure of mpg-C3N4 depending on the polycondensation temperature. Among all of the formerly reported performances in the literature (including the ones for Degussa P25 commercial benchmark), currently synthesized mpg-C3N4 photocatalysts exhibit a significantly superior visible light-induced photocatalytic activity towards rhodamine B (RhB) dye. Enhanced catalytic efficiency could be mainly attributed to the terminated polycondensation process, high specific surface area, and mesoporous structure with a wide pore size distribution.

Role of Calcination Temperature on the Hydrotalcite Derived MgO–Al2O3 in Converting Ethanol to Butanol

Abstract: In the base catalyzed ethanol condensation reactions, the calcined MgO–Al2O3 derived hydrotalcites used broadly as catalytic material and the calcination temperature plays a big role in determining the catalytic activity. The characteristics of the hydrotalcite material treated between catalytically relevant temperatures 450 and 800 °C have been studied with respect to the physical, chemical, and structural properties and compared with catalytic activity testing. With the increasing calcination temperature, the total measured catalytic basicity dropped linearly with the calcination temperature and the total measured acidity stayed the same for all the calcination temperatures except 800 °C. However, the catalyst activity testing does not show any direct correlation between the measured catalytic basicity and the catalyst activity to the ethanol condensation reaction to form 1-butanol. The highest ethanol conversion of 44 % with 1-butanol selectivity of 50 % was achieved for the 600 °C calcined hydrotalcite material.

The Environmental Photochemistry of Oxide Surfaces and the Nature of Frozen Salt Solutions: A New in Situ XPS Approach

Abstract: Recent years have witnessed fast advancements in near ambient pressure X-ray photoelectron (NAPP) spectroscopy, which is emerging as a powerful tool for the investigation of surfaces in presence of vapors and liquids. In this paper we present a new chamber for the investigation of solid/vapor interfaces relevant to environmental and atmospheric chemistry that fits to the NAPP endstation at the Swiss Light Source. The new chamber allows for performing X-ray photoelectron spectroscopy (XPS) and electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) using soft, tender and hard X-ray in vacuum and in near-ambient pressures up to 20 mbar at environmentally relevant conditions of temperature and relative humidity. In addition, the flow tube design of the chamber enables the dosing of sticky reactive gases with short pressure equilibration time. The accessible photoelectron kinetic energy ranges from 2 to 7000 eV. This range allows the determination of surface and bulk electronic properties of ice and other environmental materials, such as metal oxides and frozen solutions, which are relevant to understanding atmospheric chemistry. The design of this instrument and first results on systems of great interest to the environmental and atmospheric chemistry community are presented. In particular, near-ambient pressure XPS and NEXAFS, coupled to a UV-laser setup, were used to study the adsorption of water on a TiO2 powder sample. The results are in line with previously proposed adsorption models of water on TiO2, and, furthermore, indicate that the concentration of water molecules tends to increase upon UV irradiation. In a second example we illustrate how NEXAFS spectroscopy measurements at the chlorine K-edge can provide new insight on the structures of eutectic and sub-eutectic frozen NaCl solutions at high and low relative humidity, respectively, indicating the formation of solution and solid NaCl phases, respectively. Finally, we demonstrate the assets of this new chamber for the dosing of sticky acidic gases and, in particular, for the investigation of formic acid uptake on ice surfaces.

Sustainable Energy Systems: The Strategic Role of Chemical Energy Conversion

Abstract: In our globalized economy a multitude of energy systems are in operation. They present quite different structures and targets despite their common goal of supplying the energy needs for all societal activities reflecting the different boundary conditions of respective societies. The common quest for sustainability has given renewable electricity and “solar fuels” a high attention. The paper describes some underlying systemic aspects of integrating renewable with fossil energy and makes the point that without chemical energy conversion (CEC) this target will not be possible. A non-exhaustive list of grand challenges in CEC is derived. Some aspects of chemical energy science are discussed.

Operando Molecular Spectroscopy During Ethylene Polymerization by Supported CrO x /SiO 2 Catalysts: Active Sites, Reaction Intermediates, and Structure-Activity Relationship

Abstract: Time-resolved operando molecular spectroscopy was applied during ethylene polymerization by supported CrO x /SiO2 catalysts to investigate the structure-activity relationships for this important industrial catalytic reaction. A combination of spectroscopic techniques (Raman, UV–Vis, XAS, DRIFTS and TPSR) during ethylene polymerization allows for the first time to monitor the molecular events taking place during activation of supported CrO x /SiO2 catalysts by ethylene and establishment of the structure-activity relationships for this reaction. Based on complementary DFT computational studies, a new initiation mechanism for ethylene polymerization is proposed. During reaction, the initial surface Cr+6O x sites reduce to Cr+3 sites to form Cr–(CH2)2CH=CH2 and Cr–CH=CH2 reaction intermediates with the latter representing the catalytic active site.

Performance of Zn/ZSM-5 for In Situ Catalytic Upgrading of Pyrolysis Bio-oil by Methane

Abstract: In situ catalytic upgrading of pyrolysis oil by natural gas at atmospheric pressure was achieved over a low cost Zn/ZSM-5 catalyst. Compared with other low cost metal species including Fe, Co, Cu, Ni, Mn, Zr and Ce, ZSM-5 supported Zn obtained the highest oil yield along with high oil H/C atomic ratio and low oil O/C atomic ratio. XRD result and TEM image of the 5 % Zn/ZSM-5 catalyst showed that small ZnO particles with different sizes of <10 nm were highly dispersed on/in ZSM-5 zeolite support. Further investigation indicated that during the reaction ZSM-5 framework mainly promotes the deoxygenation and improves the quality of bio-oil, while the highly dispersed Zn species mostly facilitate CH4 activation and allow it to be incorporated into the carbon chain of the bio-oil and enhances the quantity of bio-oil. The synergistic effects between ZSM-5 framework and Zn species made this process be able to not only upgrade the quality of bio-oil, but also produce more oil product.

CO2 Hydrogenation Over Ni-Based Zeolites: Effect of Catalysts Preparation and Pre-reduction Conditions on Methanation Performance

Abstract: In this work, CO2 methanation reaction was studied on Ni-based zeolite catalysts, which were prepared by incipient wetness impregnation of USY zeolite with 5 wt% Ni. The effects of the drying method after impregnation, the calcination temperature and the pre-reduction temperature on the catalysts performances were evaluated. The catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction, diffuse reflectance UV–Vis spectroscopy (DRS UV–Vis), transmission electron microscopy and X-ray diffraction. Drying under microwaves irradiation induced remarkable changes on the type, location and reducibility of Ni species at the same time that leaded to effects in the structural and textural properties of the support and in the average nickel particle size. As a result, changes in the catalytic performances were observed. The calcination temperature changed the location and reducibility of the Ni species being concluded that calcining at 300 °C leads to higher conversions and selectivities. At high reduction temperatures the amount of reduced Ni species (active sites) was greater, but the impact of sintering processes was also stronger. For catalysts with 5 % Ni, the reduction at 550 °C was observed as the most favourable. However for 14 % Ni sample no remarkable effects were observed by reducing at higher temperatures. Thus, it was proved that CO2 conversion and CH4 selectivity can be maximised through the proper choice of both preparation and pre-reduction conditions.

Recent Approaches for Bridging the Pressure Gap in Photoelectron Microspectroscopy

Abstract: Ambient-pressure photoelectron spectroscopy (APPES) and microscopy are at the frontier of modern chemical analysis at liquid–gas, solid–liquid and solid–gas interfaces, bridging science and engineering of functional materials. Complementing the current state-of-the art of the instruments using differentially pumped analyzers, we survey in this short review several alternative APPES approaches, developed recently in the scanning photoelectron microscope (SPEM) at the Elettra laboratory. The reported set-ups allow for performing dynamic near-ambient pressure experiments without introducing additional differential pumping stages. They include implementation of pulsed-gas injection in the vicinity of samples or placing the sample inside reaction cells with very small apertures. The major part of the review is dedicated to construction and performance of novel environmental cells, where ultrathin electron-transparent but molecularly impermeable membranes are used to isolate the gas or liquid ambient from the electron detector operated in ultra-high vacuum (UHV). We demonstrate that two-dimensional materials, such as graphene and derivatives, are mechanically robust to withstand atmospheric—UHV pressure differences and are sufficiently transparent for the photoelectrons emitted from samples immersed in liquid or gaseous media. Representative results illustrate the performance of reported APPES approaches using tunable synchrotron X-rays, combined with the sub-micrometer lateral resolution of SPEM. They demonstrate the unique opportunities for addressing the chemical composition and electronic structure of surfaces and interfaces under realistic operation conditions with unprecedented lateral and spectral resolution.

ZrO2 Acting as a Redox Catalyst

Abstract: Surface defects are discussed and reviewed with regards to the use of ZrO2 in applications involving interactions with CO, H2, CH4, CO2, water and hydrocarbons. Studies of catalytic partial oxidation of methane reveal that part of the surface lattice oxygen in terraces can be removed by methane at high temperatures (e.g. 900 °C). The reaction proceeds via a surface confined redox mechanism. The studies presented here also highlight that defects play a decisive role in the water–gas-shift reaction, since the reaction is likely carried out via OH groups present at defect sites, which are regenerated by dissociating water. Hydroxyl chemistry on ZrO2 is briefly reviewed related to the studies presented. Finally, new density functional theory calculations were conducted to find out how H2S interacts with ZrO2 surface (defect sites), in order to explain enhancement of activity in naphthalene and ammonia oxidation by H2S. Molecularly adsorbed H2S as well as terminal SH species (produced by dissociation of H2S) cannot be responsible for enhanced reactivity of surface oxygen. In contrast, multi-coordinated SH induced a relatively weak increase of the reactivity of neighboring OH groups according to thermodynamic calculations. Probably, the right active site responsible for the observed H2S-induced enhancement of oxidation activity on ZrO2 is yet to be discovered.

Supported, Ligand-Functionalized Nanoparticles: An Attempt to Rationalize the Application and Potential of Ligands in Heterogeneous Catalysis

Abstract: The binding of molecules to the surface of nanoparticles (NPs) for the use as ligands to manipulate the catalytic properties of NPs is an emerging research area. Various studies with interesting results have been reported in the past few years, but it seems not clear how these findings could be merged into some kind of unified picture, describing the mechanism of action of ligands in heterogeneous catalysis. The aim of this article is to summarize some of the recent achievements in this field with focus on discussing these results using concepts from heterogeneous and homogeneous catalysis. By this it is attempted to separate the influence of ligands into (i) changing the surface properties and (ii) acting as a function above or perpendicular to the surface. The first aspect can be rationalized by the knowledge from bimetallic catalysis. In contrast, the second proposes the relevance of ligand–reactant interactions, as known from homogeneous catalysis, in order to manipulate adsorption, activation, and conversion of reactants. As the application of ligands in heterogeneous catalysis is still a young research field and the full potential of the approach still unknown, this article does not claim to give a complete summery of all results gained within this field. Instead, the author aims to present a picture that may give some guidance for future studies in this area, based on established knowledge from homo- and heterogeneous catalysis.

Ru–Ni Catalyst in the Combined Dry-Steam Reforming of Methane: The Importance in the Metal Order Addition

Abstract: Biogas is one of the main biomass-energy resources. Its use for syngas production with a H2/CO ratio close to two would have huge environmental, social and economic impact in the actual energetic scenario. However, the use of dry reforming, where the two main components are transformed into syngas, does not allow the desired H2/CO ratio. For this reason, the addition of water is proposed. The process was performed with two Ru–Ni catalysts where the metal order in the impregnation process was varied. The catalysts were prepared either by simultaneous or consecutive impregnation of the active phases and its catalytic performance in the combined dry-steam reforming of methane was tested. The catalysts were characterized by XRF, XRD, SBET, TPR-H2 and Raman spectroscopy. The existence of a strong Ni–Ru interaction is evidenced by Raman spectroscopy and TPR-H2 in the sample synthesized by the simultaneous impregnation. Concerning the catalytic activity, this sample presents the highest CH4 and CO2 conversion values in the entire composition rate and the lowest amount of carbon deposits after reaction. After pulse, and reactivity tests it was concluded that the higher Ni–Ru interaction displayed by the catalyst synthesized by the simultaneous impregnation, enhances the carbon gasification.

Evaluation of Silica-Supported Metal and Metal Phosphide Nanoparticle Catalysts for the Hydrodeoxygenation of Guaiacol Under Ex Situ Catalytic Fast Pyrolysis Conditions

Abstract: A series of metal and metal phosphide catalysts were investigated for the hydrodeoxygenation of guaiacol under ex situ catalytic fast pyrolysis conditions (350 °C, 0.5 MPa, 12 H2:1 guaiacol, weight hourly space velocity 5 h−1). Ligand-capped Ni, Pt, Rh, Ni2P, and Rh2P nanoparticles (NPs) were prepared using solution-phase synthesis techniques and dispersed on a silica support. For the metal phosphide NP-catalysts, a synthetic route that relies on the decomposition of a single molecular precursor was employed. The reactivity of the NP-catalysts was compared to a series of reference materials including Ni/SiO2 and Pt/SiO2 prepared using incipient wetness (IW) impregnation and a commercial (com) Pt/SiO2 catalyst. The NP-Ni/SiO2 catalyst exhibited the largest reduction in the oxygen mol% of the organic phase and outperformed the IW-Ni/SiO2 material. Although it was less active for guaiacol conversion than NP-Ni/SiO2, NP-Rh2P/SiO2 demonstrated the largest production of completely deoxygenated products and the highest selectivity to anisole, benzene, and cyclohexane, suggesting that it is a promising catalyst for deoxygenation of aryl-OH bonds. The com-Pt/SiO2 and IW-Pt/SiO2 catalyst exhibited the highest normalized rate of guaiacol conversion per m2 and per gram of active phase, respectively, but did not produce any completely deoxygenated products.

Photocatalytic Reduction of CO2 with Water into Methanol and Ethanol Using Graphene Derivative–TiO2 Composites: Effect of pH and Copper(I) Oxide

Abstract: Fuels derived from CO2 can contribute to neutralize the carbon balance in the atmosphere and can be converted into easily transportable liquid chemicals, such as methanol (MeOH) or ethanol (EtOH). In this work, a composite prepared from graphene oxide (GO) and titanium dioxide (TiO2) is applied to the photocatalytic water reduction of CO2 into renewable fuels under UV/vis light irradiation. The pH was identified as a key variable towards selective MeOH formation. The prepared GO–TiO2 composite exhibited superior photocatalytic activity for EtOH production (144.7 μmol g−1 h−1) at pH 11.0 and for MeOH production (47.0 μmol g−1 h−1) at pH 4.0. The effect of copper species in the GO–TiO2 composite is also assessed and its influence on the photocatalytic reaction inferred. The photocatalysts prepared with copper nitrate as copper precursor exhibited the highest rate of MeOH production at pH 11.0. Accordingly, a conceptual scheme in which the photogenerated electrons are used to reduce CO2 is proposed.

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Abstract: The design of heterogeneous selective oxidation catalysts based upon complex metal oxides is governed at present by a set of empirical rules known as “pillars of oxidation catalysis”. They serve as practical guidelines for catalyst development and guide the reasoning about the catalyst role in the process. These rules are, however, not based upon atomistic concepts and thus preclude their immediate application in for example computer-aided search strategies. The present work extends the ideas of the pillar rules and develops the concept of considering a selective oxidation catalyst as enabler for the execution of a reaction network. The enabling function is controlled by mutual interactions between catalyst and reactants. The electronic structure of the catalyst is defined as a bulk semiconductor with a surface state arising form a terminating over layer being different from the structure of the bulk. These components that can be identified by in situ analytical methods form a chemical system with feedback loops, which is responsible for generating selectivity during execution of the reaction network. This concept is based upon physical observables and could allow for a design strategy based upon a kinetic description that combines the processes between reactants with the processes between catalyst and reactants. Such kinetics is not available at present. Few of the constants required are known but many of them are accessible to experimental determination with in situ techniques.

Furfural Hydrogenation to Furfuryl Alcohol over Bimetallic Ni–Cu Sol–Gel Catalyst: A Model Reaction for Conversion of Oxygenates in Pyrolysis Liquids

Abstract: High metal loading NiCu-based catalyst of Picula™ series produced by sol–gel technique was applied to furfural hydrogenation in the presence of hydrogen. This reaction represents the stabilization of pyrolysis oil that involves the selective reduction of aldehydes and ketones to alcohols and unsaturated C–C double bonds of pyrolysis oils components. The catalysts were pre-reduced at 250 and 300 °C. According to XRD analysis results, copper is mainly in the metallic state, and Ni is mostly in the form of oxide and silicate. XPS measurements reveal that hydrogen treatment at 250 °C leads to the partial reduction of Ni to the metallic state (6 %) while further reduction at 300 °C leads to an increase in this proportion up to 39 %. A 100 % selectivity towards furfuryl alcohol was achieved at 130 °C and 5 MPa of hydrogen in a batch reactor using decyl alcohol as a solvent. In the experiments with i-propanol as a solvent at 110–170 °C the main product was furfuryl alcohol, but minor components traced back were tetrahydrofurfuryl alcohol, 2-methylfuran and isopropyl furfuryl ether. The lower catalyst reduction temperature promotes the formation of isopropyl ester, while a higher reduction temperature favors further furfuryl alcohol hydrogenation.

Methane activation by selective oxidation

Abstract: The selective activation of methane by oxidation is a topic that has fascinated scientists and engineers for over a century. In this paper some of the recent approaches will be described and discussed. In particular, the use of FeZSM5 as a catalyst for methane oxidation with aqueous hydrogen peroxide will be described. With this catalyst the primary product is methyl hydroperoxide which decomposes to give methanol. This catalyst is highly active at 50 °C but yields formic acid which is formed by the sequential oxidation of methanol. Addition of Cu either in solution or within the catalyst matrix switches off the sequential oxidation and methanol is obtained with very high selectivity. Comments are made concerning the prospects for the use of molecular oxygen as the terminal oxidant which is the preferred route.

Future Challenges and Incoming Solutions in Emission Control for Heavy Duty Diesel Vehicles

Abstract: This paper provides a review of the incoming regulations in the heavy duty diesel (HDD) area and discusses potential new catalyst technologies to enable HDD engines to meet such legislation. A major challenge is to develop combined engine + aftertreatment systems to enable optimum fuel consumption (and therefore low CO2) while meeting the legislated levels of criteria pollutants (CO, HC, NOx and particulate matter). Improved fuel consumption generally leads to higher engine-out NOx levels and lower exhaust temperatures, both of which present challenges for catalyst systems. Future emission control systems will need to enable increased NOx control under all conditions, but particularly at lower temperatures. Current HDD aftertreatment systems used in the developed markets employ the diesel oxidation catalyst + catalysed soot filter + selective catalytic reduction (SCR) + ammonia slip catalyst (ASC) architecture, and are very successful at controlling pollutant emissions. Nevertheless, as outlined above, further improvements are necessary in future. Potential approaches to meet these incoming challenges include the use of new, improved SCR catalysts, potentially extruded or combined with high porosity substrates (to enable increased catalyst loading, and therefore activity, per unit volume). Incorporating the SCR catalyst onto the diesel particulate filter to make an SCRF® component also leads to improved low temperature performance since this allows the SCR catalyst to be located closer to the engine. The cold start performance can be further enhanced by using a Diesel Cold Start Concept catalyst, which stores NOx at very low temperatures and then releases it at higher temperatures when the downstream SCR system is hot enough to convert it. This exciting new technology, and the improvement in cold start performance that it enables, is discussed in detail in this article. The final component of the system is the ASC, whose main function is to prevent the release of ammonia, slipped from the upstream SCR system, to the atmosphere. While the removal of ammonia by oxidation is relatively easy, there is a critical need to maximise the selectivity to N2 and minimise the generation of both N2O (which is a potent Greenhouse gas) and NOx (since the SCR system is used to remove NOx)—second generation ASCs are quite effective at doing this since they use a component with SCR activity as an overlayer above the principal ammonia oxidation catalyst. New catalysts under development show a further increase in the desired selectivity to N2. This article discusses the current state-of-the-art in these incoming technologies, which will enable future HDD engines to meet the dual aims of improved fuel consumption and lower pollutant emissions.

On the Structure Sensitivity of Formic Acid Decomposition on Cu Catalysts

Abstract: Catalytic decomposition of formic acid (HCOOH) has attracted substantial attention since HCOOH is a major by-product in biomass reforming, a promising hydrogen carrier, and also a potential low temperature fuel cell feed. Despite the abundance of experimental studies for vapor-phase HCOOH decomposition on Cu catalysts, the reaction mechanism and its structure sensitivity is still under debate. In this work, self-consistent, periodic density functional theory calculations were performed on three model surfaces of copper—Cu(111), Cu(100) and Cu(211), and both the HCOO (formate)-mediated and COOH (carboxyl)-mediated pathways were investigated for HCOOH decomposition. The energetics of both pathways suggest that the HCOO-mediated route is more favorable than the COOH-mediated route on all three surfaces, and that HCOOH decomposition proceeds through two consecutive dehydrogenation steps via the HCOO intermediate followed by the recombinative desorption of H2. On all three surfaces, HCOO dehydrogenation is the likely rate determining step since it has the highest transition state energy and also the highest activation energy among the three catalytic steps in the HCOO pathway. The reaction is structure sensitive on Cu catalysts since the examined three Cu facets have dramatically different binding strengths for the key intermediate HCOO and varied barriers for the likely rate determining step—HCOO dehydrogenation. Cu(100) and Cu(211) bind HCOO much more strongly than Cu(111), and they are also characterized by potential energy surfaces that are lower in energy than that for the Cu(111) facet. Coadsorbed HCOO and H represents the most stable state along the reaction coordinate, indicating that, under reaction conditions, there might be a substantial surface coverage of the HCOO intermediate, especially at under-coordinated step, corner or defect sites. Therefore, under reaction conditions, HCOOH decomposition is predicted to occur most readily on the terrace sites of Cu nanoparticles. As a result, we hereby present an example of a fundamentally structure-sensitive reaction, which may present itself as structure-insensitive in typical varied particle-size experiments.

High Temperature Interaction of Rhodium with Oxygen Storage Component in Three-Way Catalysts

Abstract: A series of three-way catalysts with Rh loading in the range of 0.01–1 wt% was prepared by incipient wetness impregnation. CeO2, CeZrO2 and ZrCeYLaO2 were used as a support. All samples were tested for catalytic activity and oxygen storage capacity function, and characterized by X-ray diffraction, surface area measurements, scanning and transmission electron microscopy, and ethane hydrogenolysis testing reaction. Rhodium was found to be in a strong interaction with ceria resulting in accelerated structure collapse at high temperatures. Ceria doped with Zr or Zr, Y and La has a minimal effect of Rh on textural changes. In all cases, surface concentration of Rh decreases in more than one order of magnitude. No phase transformation of oxygen storage component was detected by X-ray diffraction. The Rh-ceria particles with increased density were found regardless of type of the support. Coefficient of compaction for the Rh-containing catalysts diminishes in the following order: CeO2 > CeZrO2 > ZrCeYLaO2.

Hydrogen Intercalation of Graphene and Boron Nitride Monolayers Grown on Pt(111)

Abstract: H2 atmosphere is often involved in growth and application of two-dimensional (2D) atomic crystals, and it is of great importance to understand interaction of the 2D materials with H2 molecules. Here, a full graphene layer and a full hexagonal boron nitride (h-BN) layer grown on Pt(111) were exposed to H2 atmosphere, which were investigated by in situ near ambient pressure X-ray photoelectron spectroscopy and quasi in situ ultraviolet photoelectron spectroscopy. We confirm the occurrence of hydrogen intercalation of the graphene and h-BN overlayers in ambient pressure H2. The hydrogen intercalation in 0.1 Torr H2 at room temperature and hydrogen desorption in 0.1 Torr H2 at 200 °C are fully reversible on the graphene/Pt(111) and h-BN/Pt(111) surfaces. Furthermore, hydrogen desorption on the graphene/Pt(111) and h-BN/Pt(111) surfaces was found to happen at lower temperature than that on the Pt(111) surface due to the graphene and h-BN cover effect.

Photochemical Hydrogen Production with Metal–Organic Frameworks

Abstract: Metal-Organic Frameworks (MOFs) have attracted increasing attention for the creation of solid-state platforms for catalysis applications. In this review article, we present strategies to employ MOF ...

Catalytic Pyrolysis of Pine Over HZSM-5 with Different Binders

Abstract: Three HZSM-5 catalysts with different binders (alumina, silica, and clay) were evaluated for upgrading of pine pyrolysis vapors. All catalysts were based on the same HZSM-5 with silica to alumina molar ratio of 30. Experiments in micro-scale analytical Py-GCMS/FID showed that fresh catalysts with silica and clay produced predominantly aromatic hydrocarbons at similar carbon yields. The catalyst with alumina gave lower vapor yields and produced both hydrocarbons and partially deoxygenated products, in particular furans. The catalyst with alumina also gave higher coke yields and exhibited faster deactivation than the catalysts with clay and silica binders. The low hydrocarbon yields and coke formation were attributed to the acidic sites provided by alumina and blocking of the zeolite sites. The catalysts with silica and clay as binders were further tested in a 2-inch fluidized bed system for ex situ catalytic pyrolysis of pine. Similar oils were produced over both catalysts with carbon yields of approximately 23 % and oxygen contents of 20–21 %.

Impact of the Desilication Treatment of Y Zeolite on the Catalytic Cracking of Bulky Hydrocarbon Molecules

Abstract: Mesoporosity was induced on a USY zeolite by means of an alkaline leaching process. Samples were immersed in 0.05, 0.10 and 0.20 M NaOH solutions during 15 min at room temperature and then were exchanged with NH4 + ions and calcined to yield the acid forms. The formation of mesopores with size ranging from 20 to 100 A increased with the concentration of NaOH. The modified zeolites were used at 30 wt% to formulate cracking catalysts with an inert SiO2 matrix. The catalytic performance of these catalysts in the conversion of 1,3,5-tri-isopropylbenzene was evaluated in a batch, fluidized bed reactor at 450, 500 and 530 °C, with a catalyst to oil relationship of 4.7 and contact times up to 16 s. The catalysts with the modified zeolites were more active in the cracking of these bulky molecules than the one with the parent, unmodified zeolite; moreover, the selectivity to the products of primary cracking reactions increased. These results reveal an enhanced diffusion of the reactant molecules to the zeolite active sites and of the products out of the catalyst particles.

On the role of water in heterogeneous catalysis:a tribute to Professor M. Wyn Roberts

Abstract: From the earliest studies of heterogeneous catalysis, it was apparent that water plays a more important role in many systems than simply acting as a solvent. Its wide ranging effects have attracted increasing attention in recent years and was the topic of Prof. M.W. Roberts’ final paper. The present review explores some of the latest work on water in reactions ranging from CO oxidation to Fischer Tropsch catalysis, the different mechanisms proposed for its role are discussed and compared.