Showing papers in "Topics in Catalysis in 2009"

Impact of Zeolites on the Petroleum and Petrochemical Industry

Abstract: The general features of zeolites that led to their widespread use in oil refining and petrochemistry are highlighted as well as the details of their impact on selected processes. The analysis of the catalyst market and the position of zeolites therein is a good indication of their strategic importance. Zeolites have brought many disruptive changes to these fields (e.g. FCC). They impacted also these industries in an equally important way, although more subtle, by incremental improvement of processes. The new and vast challenges facing oil refining and petrochemistry as well as the managed transition to sustainable environmental benign transport fuel industries and chemical industries will require creative science and technologies. Zeolites offer the basis of many of these technological solutions provided efficient and balanced cooperations between industry and academia are further developed.

Aromatic Production from Catalytic Fast Pyrolysis of Biomass-Derived Feedstocks

Abstract: The conversion of biomass compounds to aromatics by thermal decomposition in the presence of catalysts was investigated using a pyroprobe analytical pyrolyzer The first step in this process is the thermal decomposition of the biomass to smaller oxygenates that then enter the catalysts pores where they are converted to CO, CO2, water, coke and volatile aromatics The desired reaction is the conversion of biomass into aromatics, CO2 and water with the undesired products being coke and water Both the reaction conditions and catalyst properties are critical in maximizing the desired product selectivity High heating rates and high catalyst to feed ratio favor aromatic production over coke formation Aromatics with carbon yields in excess of 30 molar carbon% were obtained from glucose, xylitol, cellobiose, and cellulose with ZSM-5 (Si/Al = 60) at the optimal reactor conditions The aromatic yield for all the products was similar suggesting that all of these biomass-derived oxygenates go through a common intermediate At lower catalyst to feed ratios volatile oxygenates are formed including furan type compounds, acetic acid and hydroxyacetaldehyde The product selectivity is dependent on both the size of the catalyst pores and the nature of the active sites Five catalysts were tested including ZSM-5, silicalite, beta, Y-zeolite and silica–alumina ZSM-5 had the highest aromatic yields (30% carbon yield) and the least amount of coke

Solvent Effects on Fructose Dehydration to 5-Hydroxymethylfurfural in Biphasic Systems Saturated with Inorganic Salts

Abstract: Furan derivatives, such as 5-hydroxymethylfurfural (HMF), obtained from acid-catalyzed dehydration of carbohydrates, can serve as renewable chemical platforms for the production of fuels and chemical intermediates. Addition of an inorganic salt to concentrated aqueous solutions of fructose (30 wt% fructose on salt free basis) in biphasic systems containing an organic extracting phase improves HMF yields by increasing the partitioning of HMF into the extracting phase, as measured by the partition coefficient, R, equal to the concentration of HMF in the organic phase normalized by the concentration in the aqueous phase. We have studied the impact of solvent choice on HMF yield using primary and secondary alcohols, ketones, and cyclic ethers in the C3–C6 range as extracting solvents in biphasic systems saturated with NaCl. Biphasic systems containing C4 solvents generated the highest HMF yields within each solvent class. Tetrahydrofuran demonstrated the best combination of high HMF selectivity (83%) and high extracting power (R = 7.1) at 423 K. The presence of NaCl provided the additional benefit of creating biphasic systems using solvents that are completely miscible with water in the absence of salt. We have also studied the impact of different salts on HMF yield in systems using 1-butanol as the extracting solvent. Na+ and K+ showed the best combination of extracting power and HMF selectivity of the monovalent and divalent chloride salts tested. Changing the anion of the salt from Cl− to Br− resulted in R-values and HMF selectivity values resembling the non-salt system, while changing to the SO42− divalent species generated a high R-value (8.1), but a low HMF selectivity value (71%).

Hydroprocessing of Bio-Oils and Oxygenates to Hydrocarbons. Understanding the Reaction Routes

Abstract: To produce diesel fuel from renewable organic material such as vegetable oils, it has for a number of years been known that triglycerides can be hydrogenated into linear alkanes in a refinery hydrotreating unit over conventional sulfided hydrodesulfurization catalysts. A number of new reactions occur in the hydrotreater, when a biological component is introduced, and experiments were conducted to obtain a more detailed understanding of these mechanisms. The reaction pathways were studied both in model compound tests and in real feed tests with mixtures of straight-run gas oil and rapeseed oil. In both sets of experiments, the hydrogenation of the oxygen containing compounds was observed to proceed either via a hydrodeoxygenation (HDO) route or via a decarboxylation route. The detailed pathway of the HDO route was further illuminated by studying the hydroprocessing of methyl laurate into n-dodecane. The observed reaction intermediates did not support a simple stepwise hydrogenation of the aldehyde formed after hydrogenation of the connecting oxygen in the ester. Instead, it is proposed that the aldehyde formed is enolized before further hydrogenation. The existence of an enol intermediate was further corroborated by the observation that a ketone lacking α-hydrogen (that cannot be directly enolized) had a much lower reactivity than a corresponding ketone with α-hydrogen. In real feed tests, the complete conversion of rapeseed oil into linear alkanes at mild hydrotreating conditions was demonstrated. From the gas and liquid yields, the relative rates of HDO and decarboxylation were calculated in good agreement with the observed distribution of the n-C17/n-C18 and n-C21/n-C22 formed. The hydrogen consumption associated with each route is deduced, and it was shown that hydrogen consumed in the water-gas-shift and methanization reactions may add significant hydrogen consumption to the decarboxylation route. The products formed exhibited high cetane values and low densities. The challenges of introducing triglycerides in conventional hydrotreating units are discussed. It is concluded that hydrotreating offers a robust and flexible process for converting a wide variety of alternative feedstocks into a green diesel fuel that is directly compatible with existing fuel infrastructure and engine technology.

Catalytic Applications of Zeolites in Chemical Industry

Abstract: New materials are prerequisite for major breakthrough applications influencing our daily life, and therefore are pivotal for the chemical industry. Nanoporous materials constitute an important class of heterogeneous catalysts as they not only offer higher surface areas and enhanced activity, but also provide shape/size selectivity. As a well-established family of nanoporous materials, zeolites are of paramount importance for the chemical industry as heterogeneous catalysts with shape/size-selective character in various reactions. Zeolites can also play an active role in the quest for raw material change as catalysts providing the required selectivity towards base chemicals. In this contribution, an overview of the current and potential applications of zeolites as catalysts in chemical industry is presented.

The Effect of Acid Strength on the Conversion of Methanol to Olefins Over Acidic Microporous Catalysts with the CHA Topology

Abstract: The present work addresses the influence of acid strength on the stability and product selectivity of microporous catalysts with CHA framework type The two studied catalysts, H-SAPO-34 and H-SSZ-13, have the same topology, density of acid sites (approximately one acid site per cage), and crystal size (02–2 microns), but their acid strength differ due to the framework composition The difference in acid strength was determined by infrared spectroscopy, using CO as probe molecule Catalytic tests were performed in a fixed bed flow reactor at 300–425 °C and WHSV = 60 h−1 It was observed that the acid strength has significant influence on reaction rates, enhancing the production rate of olefins in the reactor effluent as well as aromatics retained in the catalyst pores and leading to a lower optimal temperature of operation for the more acidic H-SSZ-13 catalyst The activation and deactivation patterns and the intermediates formed are very similar for the two materials The ethene to propene ratio increases with temperature and time on stream for both catalysts, and is higher over the more acidic H-SSZ-13 catalyst at similar reaction conditions

Nitrogen-Containing Carbon Nanostructures as Oxygen-Reduction Catalysts

Abstract: Nitrogen-containing carbon nanostructure (CNx) catalysts developed by acetonitrile pyrolysis have been studied to better understand their role in the oxygen reduction reaction (ORR) in PEM and direct methanol fuel cell environments. Additional functionalization of the CNx catalysts with nitric acid has the ability to improve both the activity and selectivity towards ORR.

Hydrolysis of Cellulose Selectively into Glucose Over Sulfonated Activated-Carbon Catalyst Under Hydrothermal Conditions

Abstract: A sulfonated activated-carbon (AC-SO3H) catalyst selectively hydrolyzes cellulose with β-1,4-glycosidic bonds into glucose in the catalytic hydrothermal reactions at temperatures around 423 K. The AC-SO3H catalyst with the hydrothermal pre-treatment has the excellent catalytic properties attributed to the high hydrothermal stability and the strong acid sites of sulfo functional groups.

Transformation of Vegetable Oils into Hydrocarbons over Mesoporous-Alumina-Supported CoMo Catalysts

Abstract: Deoxygenation of triglycerides over organized-mesoporous-alumina-supported CoMo catalysts (CoMo/OMA) has been investigated in this work. CoMo/OMA catalysts exhibited higher activity for deoxygenation of triglycerides than CoMo supported on MCM-41 (silica) and ordinary alumina supports. Two main deoxygenation pathways were found: hydrodeoxygenation and hydrodecarboxylation. Their extent was affected by reaction temperature, pressure and the support used. Hydrodeoxygenation was the main reaction under the studied conditions. The extent of hydrodecarboxylation increased with increasing reaction temperature and decreasing reaction pressure.

Production of Biomass-Derived Chemicals and Energy: Chemocatalytic Conversions of Glycerol

Abstract: The growing production of biodiesel as a renewable source-based fuel leads to an increased amount of glycerol. Thus, it is a favorable starting material to obtain highly functionalized products. From a variety of catalytic reactions three examples, namely glycerol oxidation, glycerol hydrogenolysis and aqueous-phase reforming, were chosen for detailed studies in our group. The experimental focus for the oxidation of glycerol was set on preparation and detailed examination of supported Pt-Bi catalysts in batch reactions as well as in continuous experiments using a trickle bed reactor. For aqueous-phase reforming of glycerol to hydrogen the addition of tin to supported platinum catalysts was investigated. Ruthenium and copper based catalysts could be successfully applied in the hydrogenolysis of glycerol to 1,2-propanediol.

Co–Ni Catalysts Derived from Hydrotalcite-Like Materials for Hydrogen Production by Ethanol Steam Reforming

Abstract: A series of Co–Ni catalysts, prepared from hydrotalcite (HT)-like materials by co-precipitation, has been studied for the hydrogen production by ethanol steam reforming. The total metal loading was fixed at 40% and the Co–Ni composition was varied (40–0, 30–10, 20–20, 10–30 and 0–40). The catalysts were characterized using X-ray diffraction, N2 physisorption, H2 chemisorption, temperature-programmed reduction, scanning transmission electron microscope and energy dispersive spectroscopy. The results demonstrated that the particle size and reducibility of the Co–Ni catalysts are influenced by the degree of formation of a HT-like structure, increasing with Co content. All the catalysts were active and stable at 575 °C during the course of ethanol steam reforming with a molar ratio of H2O:ethanol = 3:1. The activity decreased in the order 30Co–10Ni > 40Co ~ 20Ni–20Co ~ 10Co–30Ni > 40Ni. The 40Ni catalyst displayed the strongest resistance to deactivation, while all the Co-containing catalysts exhibited much higher activity than the 40Ni catalyst. The hydrogen selectivities were high and similar among the catalysts, the highest yield of hydrogen was found over the 30Co–10Ni catalyst. In general, the best catalytic performance is obtained with the 30Co–10Ni catalyst, in which Co and Ni are intimately mixed and dispersed in the HT-derived support, as indicated by the STEM micrograph and complementary mapping of Co, Ni, Al, Mg and O.

Selective Oxidation Catalysis: Opportunities and Challenges

Abstract: This contribution discusses some aspects crucial for designing optimal and sustainable oxidation processes. The catalyst, although at the heart of the system, is only one decisive design parameter amongst many others. Indeed, an interdisciplinary approach is required to improve existing processes, but also to rationally and systematically access opportunities for oxidation research on renewable feedstock compounds.

Role of B5-Type Sites in Ru Catalysts used for the NH3 Decomposition Reaction

Abstract: A series of activated carbon supported Ru catalysts have been reduced at different temperatures under hydrogen flow, and in some cases under ammonia flow, in order to modify the morphology and the particle size of the metallic active sites. CO chemisorption and transmission electron microscopy have been applied to follow the variations of these particles. The samples have been tested in the ammonia decomposition reaction, where systematic differences in catalytic activities as consequence of the support modification as well as due to the changes in the Ru particle sizes have been detected. Furthermore when potassium is added as catalyst promoter the sintering of Ru particles is significantly diminished and thus the changes in catalytic activities are inhibited. The electronic states of the Ru particles have been evaluated by determination of the chemisorption heats of the CO probe molecule. A part of other promoter or support effects it seems to exit a critical mean size for Ru particles on where maximum of catalytic activity is achieved. This behavior can be rationalized by the presence of surface highly active B5 sites, which consist of an arrangement of three Ru atoms in one layer and two further Ru atoms in an internal layer. These especial surface sites are expected to be in a higher proportion over Ru crystallites of those critical sizes, namely for Ru diameter sizes in the rage of 3–5 nm.

Hydrogenolysis of Glycerol to Propanediols Over Highly Active Ru–Re Bimetallic Catalysts

Abstract: Several supported Ru–Re bimetallic catalysts (Ru–Re/SiO2, Ru–Re/ZrO2, Ru–Re/TiO2, Ru–Re/H-β, Ru–Re/H–ZSM5) and Ru monometallic catalysts (Ru/SiO2, Ru/ZrO2, Ru/TiO2, Ru/H-β, Ru/H–ZSM5) were prepared and their catalytic performances were evaluated in the hydrogenolysis of glycerol to propanediols (1,2-propanediol and 1,3-propanediol) with a batch type reactor (autoclave) under the reaction conditions of 160 °C, 8.0 MPa and 8 h. Compared with Ru monometallic catalysts, the Ru–Re bimetallic catalysts showed much higher activity in the hydrogenolysis of glycerol, and Re exhibited obvious promoting effect on the performance of the catalysts. The supported Ru monometallic catalysts and Ru–Re bimetallic catalysts were characterized by N2 adsorption/desorption, XRD, TEM-EDX, H2-TPR and CO chemisorption for obtaining some physicochemical properties of the catalysts, such as specific surface areas, crystal phases, morphologies/microstructure, reduction behaviors and dispersion of Ru metal. The results of XRD and CO chemisorption indicate that the addition of Re component could improve the dispersion of Ru species on supports. The measurements of H2-TPR revealed that the coexistence of Re and Ru components on supports changed the respective reduction behavior of Re or Ru alone on the supports, indicating the existence of synergistic effect between Ru and Re species on the bimetallic catalysts. The hydrogenolysis of some products (such as 1,2-propanediol, 1,3-propanediol, 1-propanol and 2-propanol) were also examined over Ru and Ru–Re catalysts for evaluating influence of Re–Re on the reaction routes during glycerol hydrogenolysis. The results showed that over Ru–Re catalysts, glycerol was favorable to be converted to 1,2-propanediol, but not favorable to ethylene glycol, while 1,2-propanediol and 1,3-propanediol were favorable to be converted to 1-propanol. The influence of glycerol concentration in its aqueous solution on the catalytic performance was also evaluated over Ru and Ru–Re catalysts.

NH3–NO/NO2 SCR for Diesel Exhausts Aftertreatment: Reactivity, Mechanism and Kinetic Modelling of Commercial Fe- and Cu-Promoted Zeolite Catalysts

Abstract: The activity and the mechanism of the main reactions in the NO/NO2–NH3 SCR reacting system were comparatively investigated over a Fe- and a Cu-promoted commercial zeolite catalyst for the aftertreatment of Diesel exhausts. A dynamic micro-kinetic model in close agreement with all the details of the SCR catalytic chemistry was also developed.

Chemicals from Biomass: Aerobic Oxidation of 5-Hydroxymethyl-2-Furaldehyde into Diformylfurane Catalyzed by Immobilized Vanadyl-Pyridine Complexes on Polymeric and Organofunctionalized Mesoporous Supports

Abstract: Diformylfurane (DFF) has been obtained by aerobic oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) with homogeneous pyridine-vanadyl complexes in homogeneous phase, with Cu and V in poly(4-vinylpyridine) crosslinked with 33% divinylbenzene (PVP) and supported on organofunctionalized SBA-15 mesoporous materials. Detailed spectroscopic characterization of the materials is provided. Catalytic results show that pyridine-vanadyl complexes supported on SBA-15 are less active than when in the polymeric form. The nature of the catalyst surface and solvent plays a key role on the catalytic behaviour.

From Renewable to Fine Chemicals Through Selective Oxidation: The Case of Glycerol

Abstract: Catalytic selective oxidation of glycerol is presented in terms of catalytic systems and experimental conditions. Unsupported gold nanoparticles (AuNPs), AuNPs on carbon and on TiO2 were employed and compared in terms of reaction selectivity and activity. The role of the base and the formed hydrogen peroxide has been considered. Gold based catalysts showed selectivity that is strongly dependent of the reaction conditions. In particular C–C scission products increases by increasing the reaction temperature but correlated only partially with the rate of degradation of the H2O2 formed under the operative conditions. Moreover, under neutral/acidic conditions glycerol can be oxidised also by increasing the temperature slightly, but it leads to a detrimental effect on selectivity and catalyst life.

Catalysis: Role and Challenges for a Sustainable Energy

Abstract: After introducing the role of catalysis as pillar of chemical industry to reach the sustainability of the society, the contribution discusses catalysis for energy as one of the critical areas of development to respond to societal needs and which further demonstrate the link between catalysis, innovation and sustainability. In particular, some aspects of development of catalysts for the photo- and electro-driven conversion of carbon dioxide and water are analyzed. In PEM fuel cells, advanced anode electrocatalysts with improved performances and reduced sensitivity to poisoning by CO could be developed by proper understanding of the role of nanostructure, three phase boundary and metal particle-carbon substrate interaction. It is shown also that similar materials could be used for addressing the societal challenge of converting back CO2 to fuels. New results on the electrocatalytic conversion of carbon dioxide to liquid fuels (isopropanol, in particular) are reported and it is evidenced how in perspective, by combining these electrodes to a nanostructured titania photoanode, it is possible to realize photoelectrocatalytic devices which have the potential to capture CO2 and convert it to liquid fuels (long-chain alcohols and hydrocarbons) using solar energy and water in “artificial energy trees”.

Synthesis and Characterization of Manganese Oxide Catalysts for the Total Oxidation of Ethyl Acetate

Abstract: Manganese oxide catalysts were synthesized by direct reaction between manganese acetate and permanganate ions, under acidic and reflux conditions. Parameters such as pH (2.0–4.5) and template cation (Na+, K+ and Cs+) were studied. A pure cryptomelane-type manganese oxide was synthesized under specific conditions, and it was found that the template cation plays an important role on the formation of this kind of structure. Cryptomelane was found to be a very active oxidation catalyst, converting ethyl acetate into CO2 at low temperatures (220 °C). This catalyst is very stable at least during 90 h of reaction and its performance is not significantly affected by the presence of water vapour or CO2 in the feed stream. The catalyst performance can be improved by the presence of small amounts of Mn3O4.

Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Abstract: Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M x O y ) catalysts dispersed on high surface area γ-Al2O3. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M x O y crystallite size (XRD) and reducibility (H2-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M x O y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO2 being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al2O3. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M x O y on high surface area inert supports, such as Al2O3, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M x O y /Al2O3 catalysts can be optimized by proper selection of M x O y loading. Best performing catalysts of this series include 60% MnO, 90% CeO2 and 5% CuO on Al2O3 which, under the present experimental conditions, are able to completely convert toluene toward CO2 at temperatures lower than 350 °C. Dispersion of Pt on M x O y /Al2O3 catalysts improves significantly the catalytic performance of irreducible M x O y but does not alter appreciably the activity of reducible M x O y /Al2O3 catalysts.

Direct Catalyst Monitoring by Electrical Means: An Overview on Promising Novel Principles

Abstract: By measuring the electrical properties of the catalyst coating itself, one can observe directly and in situ the state of TWC, LNT, and SCR catalysts. Two principles are possible: a contact method, for which the coating is applied to planar electrodes and the electrical impedance is measured, and a non-contact method, in which the coating material is penetrated by radio frequency waves. In either case, the catalyst state is directly correlated with the measured transmission or reflection characteristics of the electrical sensors.

The Application of Zeolites and Periodic Mesoporous Silicas in the Catalytic Conversion of Synthesis Gas

Abstract: In the recent years there has been a rising interest in the conversion of remote and abundant natural gas as well as renewable biomass sources into high quality fuels and valuable raw chemicals via synthesis gas (syngas, CO + H2) as a versatile intermediate. The metal catalysed CO hydrogenation can be selectively directed towards hydrocarbons as precursors of ultra clean liquid fuels (Fischer-Tropsch synthesis) or to added-value products such as light olefins and oxygenates (alcohols, carboxylic acids, ethers, etc.). By taking advantage of their unique and tunable structural and chemical properties, inorganic molecular sieves such as zeolites and periodic mesoporous silicas have been extensively explored as effective components of heterogeneous catalysts for the selective conversion of syngas. Thus, ordered mesoporous silicas (MCM-41, MCM-48, SBA-15) have shown interesting properties as catalytic supports for Co and Fe based Fischer-Tropsch catalysts. Besides, zeolite-entrapped mono and bimetallic clusters have been reported to selectively direct the synthesis towards oxygenates. In this work, the use of the original structural properties of these materials to tailor the dispersion, geometrical location and chemical state of metallic sites leading to heterogeneous catalysts with enhanced activity and selectivity in syngas catalytic routes is reviewed. The introduced peculiarities, benefits and drawbacks of these structured solids in comparison to conventional amorphous supports are also discussed.

Green Catalysis with Alternative Feedstocks

Abstract: The use of renewable feedstocks, derived from biomass, for the chemical industry is discussed. The modern chemical industry is based around platform chemicals, e.g. ethene, propene, benzene and xylenes, which are readily derived from oil, and using these intermediates a broad range of finished products can be derived. While it is feasible that biomass can be converted to syngas and hence to existing key platform chemicals, this loses all of the chemical complexity that is inherent in bio-derived molecules. In this paper some of the options are considered and, in particular, the oxidation of glucose and glycerol using gold nanoparticles supported on carbon is described. We also contrast the oxidation of glycerol using supported gold and gold-palladium alloys prepared using an impregnation technique, since the gold-palladium alloys have been shown to be highly effective for the oxidation of alcohols and the synthesis of hydrogen peroxide.

Suppression of Noble Metal Sintering Based on the Support Anchoring Effect and its Application in Automotive Three-Way Catalysis

Abstract: Suppression of noble metal sintering is a very important approach in the development of automotive three-way catalysts. The investigation into the Pt sintering behavior revealed that the formed Pt–O–M (M: cation of oxide, i.e., cerium oxide) bond acted as an anchor to suppress the Pt sintering, and that the strength of the Pt-oxide-support interaction was well correlated with the electron density of oxygen in the support oxide. To achieve a good balance between catalytic activity and the sintering suppression, ceria based oxide support was verified to be suitable for Pt, and zirconia based oxide support was appropriate support for Rh. Through optimizing the configuration of Pt and Rh in the catalyst, a novel three-way catalyst was developed successfully, and this catalytic activity is far superior to the conventional catalyst, but with lower noble metal content.

Co–Mg–Al Hydrotalcite Precursors for Catalytic Total Oxidation of Volatile Organic Compounds

Abstract: Co–Mg–Al hydrotalcite type solids were synthesized as precursors of catalysts for the total oxidation of toluene. After calcination at 500 °C, different mesoporous mixed oxides were obtained with high specific surfaces. The comparison of the catalytic activities of the calcined hydrotalcites with those of calcined hydroxides evidenced the superiority of the first oxides explained meanly by higher specific surfaces and more easily reducible particles. DRIFT “operando” allowed to follow the oxidation reaction and the formation of light coke and carbonate species.

Nano-Particles in Heterogeneous Catalysis

Abstract: The introduction of in situ techniques has had a vast impact on research and development in the area of heterogeneous catalysis as emphasized in many reviews and monographs. Recently, the number of in situ techniques that can give information at the atomic scale has increased significantly and new possibilities exist for making the measurements under industrially relevant conditions. In order to fully exploit the results from the in situ and operando studies, it has also become increasingly gainful to combine the experimental studies with theoretical methodologies based on, for example, Density Functional Theory (DFT). This has allowed one to extract more detailed atomic-scale information from the measurements and it has also allowed the establishment of detailed structure-activity relationships. Furthermore, the interplay between in situ techniques and theory has helped bridging the pressure gap such that in situ information obtained at conditions far from industrial ones may be used in a more relevant manner. Here, we will illustrate how microscopy-, spectroscopy- and X-ray-based techniques in combination with experimental and theoretical surface science methods can aid industrial catalyst developments. We will do this by presenting examples of our current understanding and latest developments in the areas of heterogeneous nano-particle catalysts for methanol synthesis, steam reforming and hydrotreating.

Supported Nano-Gold Catalysts for Epoxidation of Styrene and Oxidation of Benzyl Alcohol to Benzaldehyde

Abstract: Nano-gold particles supported on different alkaline earth oxides (viz. MgO, CaO, BaO and SrO), Gr. IIIa metal oxides (viz. Al2O3, Ga2O3, In2O3 and Tl2O3), transition metal oxides (viz. TiO2, Cr2O3, MnO2, Fe2O3, CoOx, NiO, CuO, ZnO, Y2O3 and ZrO2), rare earth metal oxides (viz. La2O3, Ce2O3, Nd2O3, Sm2O3, Eu2O3, Tb2O3, Er2O3 and Yb2O3) and U3O8 [all prepared by depositing gold on corresponding metal oxide support by deposition precipitation (DP) and/or homogeneous deposition precipitation (HDP) method] were evaluated for their catalytic performance in the liquid phase epoxidation of styrene by tert-butyl hydroperoxide (TBHP) to styrene oxide and also in the solvent-free benzyl alcohol-to-benzaldehyde oxidation (by molecular oxygen or TBHP) reactions. For the epoxidation, the catalytic performance (styrene oxide yield) of the most promising nano-gold catalysts prepared by the HDP method was in the following order: Au/MgO > Au/Tl2O3 > Au/Yb2O3 > Au/Tb2O3 > Au/CaO (or TiO2). However, for the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen, the order of choice for the most promising catalysts (based on benzaldehyde yield) was Au/U3O8 > Au/Al2O3 > Au/ZrO2 > Au/MgO. Whereas, when TBHP was used as an oxidizing agent for the benzyl alcohol oxidation, the order of choice for the most promising catalysts was Au/U3O8 > Au/MgO > Au/TiO2 > Au/ZrO2 > Au/Al2O3. The catalytic performance of a particular supported nano-gold catalyst was thus found to depend on the reaction catalysed by them. Moreover, it is strongly influenced by a number of catalyst parameters, such as the metal oxide support, the method of gold depositon on the support, the gold loading and also on the catalyst calcination temperature. Nano-gold particles-support interactions seem to play an important role in controlling the deposition of gold (amount of gold deposited and size and morphology of gold particles), formation of different surface gold species (Au0, Au1+ and Au3+) and electronic properties of gold particles and, consequently, control the catalytic performance (both the activity and selectivity) of the supported nano-gold catalysts in the reactions. The nano-gold catalysts prepared by the HDP method showed much better catalytic performance than those prepared by the DP, coprecipitation or impregnation method; in general, the HDP method provided supported gold catalysts with much higher gold loading and/or smaller size gold particles than that achieved by the DP and other methods.

Revisiting the Behaviour of Vanadia-Based Catalysts in the Abatement of (Chloro)-Aromatic Pollutants: Towards an Integrated Understanding

Abstract: For several years, the authors study VO x /TiO2 catalytic formulations in the context of the oxidative abatement of aromatics, possibly chlorinated, from polluted air. This paper revisits their main findings and understandings. Although VO x /TiO2 catalysts, when upgraded with Mo or W oxides, are already used in industrial applications, it is shown that the systematic investigation (i) of the reasons why optimized synthesis and formulations are indeed efficient, (ii) of the nature of the sites responsible for the adsorption of the pollutants and their catalytic transformation, and (iii) of the corresponding mechanisms, is a valuable approach to identify guidelines and strategies for further improving the catalysts. The origin of the beneficial effects brought by WO x and MoO x to VO x /TiO2, and by the use of a sulphated titania support, is addressed, as well as the impact on the catalysts behaviour and performances of molecules inevitably present in a combustion exhaust gas, like CO and NO x co-pollutants and water. The behaviours of a chloro-aromatic molecule, like chlorobenzene, and an oxygen containing-heterocyclic molecule, like furan and dimethylfuran, are then compared and discussed in the debate of their selection as representative model compounds for the catalytic abatement of dioxins. In this context, it is shown that strategies developed to improve the performances of VO x /TiO2 formulations to abate Cl-aromatics, could be detrimental for cyclic molecules containing O-heteroatom, as entire dioxins. Finally, an integrated view of the catalytic process is presented by envisaging the case of a complex mixture, closer to the real application of gaseous effluent cleaning.

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

Abstract: Knowledge of gradients involved in chemical processes, such as heterogeneously catalyzed reactions, on molecular as well as reactor scale is of paramount importance for understanding and optimizing such processes. This review highlights and discusses recent advances in spatially resolved methods for the detection of chemical (structural) and temperature gradients, with particular focus on in situ methods.

Applying Dynamic and Synchronous DRIFTS/EXAFS to the Structural Reactive Behaviour of Dilute (≤1 wt%) Supported Rh/Al2O3 Catalysts using Quick and Energy Dispersive EXAFS

Abstract: Examples of the application of a synchronous DRIFTS/EXAFS/mass spectrometry (MS) methodology to the study of dilute (≤ 1wt%) Rh/Al2O3 catalysts are discussed. These are used to explore the potential of this approach for understanding of the behaviour of supported metal catalysts “in a single shot”, and in the often preferred regime of low (<1 wt%) loadings of active precious metals. Firstly, the sequential interaction of NO (323 K) and then CO (373 K) with reduced, 0.5 wt% Rh/Al2O3 catalysts is studied. Infrared spectroscopy indicates that two surface species (a bent Rh(NO−) and Rh(CO)2 species) can be created using this sequential gas absorption/reaction method with minimal interference from other carbonyl or nitrosyl species. As such the potential for a reliable structural characterisation of the local structure of these species by EXAFS becomes possible. However, in contrast to the infrared spectroscopy, analysis of the EXAFS data also indicates that, even for such low loaded Rh systems, oxidative disruption of the Rh by the NO and CO is not complete and that bonding typical of small Rh clusters persists in both cases. The possible sources of this apparent spectroscopic difference of opinion are discussed. Secondly, 1wt% Rh/Al2O3 catalysts are studied using dispersive EXAFS at 573 K with 100 ms time resolution, during a redox switching event involving a reducing feedstock comprising just 3000 ppm of CO and 3000 ppm of NO. It is shown that highly useful and insightful time resolved and synchronously obtained XANES/EXAFS/IR data can be obtained even in this dilute Rh and more “realistic” case. Additional data, regarding the overall performance of the experiment, as currently implemented at the ESRF, along with a discussion of where enhanced performance might be yet still be gained, are also given.