Showing papers in "Applied Catalysis A-general in 2011"

A review of catalytic upgrading of bio-oil to engine fuels

Abstract: As the oil reserves are depleting the need of an alternative fuel source is becoming increasingly apparent. One prospective method for producing fuels in the future is conversion of biomass into bio-oil and then upgrading the bio-oil over a catalyst, this method is the focus of this review article. Bio-oil production can be facilitated through flash pyrolysis, which has been identified as one of the most feasible routes. The bio-oil has a high oxygen content and therefore low stability over time and a low heating value. Upgrading is desirable to remove the oxygen and in this way make it resemble crude oil. Two general routes for bio-oil upgrading have been considered: hydrodeoxygenation (HDO) and zeolite cracking. HDO is a high pressure operation where hydrogen is used to exclude oxygen from the bio-oil, giving a high grade oil product equivalent to crude oil. Catalysts for the reaction are traditional hydrodesulphurization (HDS) catalysts, such as Co–MoS2/Al2O3, or metal catalysts, as for example Pd/C. However, catalyst lifetimes of much more than 200 h have not been achieved with any current catalyst due to carbon deposition. Zeolite cracking is an alternative path, where zeolites, e.g. HZSM-5, are used as catalysts for the deoxygenation reaction. In these systems hydrogen is not a requirement, so operation is performed at atmospheric pressure. However, extensive carbon deposition results in very short catalyst lifetimes. Furthermore a general restriction in the hydrogen content of the bio-oil results in a low H/C ratio of the oil product as no additional hydrogen is supplied. Overall, oil from zeolite cracking is of a low grade, with heating values approximately 25% lower than that of crude oil. Of the two mentioned routes, HDO appears to have the best potential, as zeolite cracking cannot produce fuels of acceptable grade for the current infrastructure. HDO is evaluated as being a path to fuels in a grade and at a price equivalent to present fossil fuels, but several tasks still have to be addressed within this process. Catalyst development, understanding of the carbon forming mechanisms, understanding of the kinetics, elucidation of sulphur as a source of deactivation, evaluation of the requirement for high pressure, and sustainable sources for hydrogen are all areas which have to be elucidated before commercialisation of the process.

Catalytic cracking of hydrocarbons over modified ZSM-5 zeolites to produce light olefins: A review

Abstract: Steam cracking of hydrocarbons has been the major source of light olefins for more than half a century. The recent studies have reported that ethylene and propylene can also be produced through the cracking of hydrocarbons over modified ZSM-5 zeolites in a considerable amount. This paper highlights the important current ideas about acid-catalyzed hydrocarbon cracking that has resulted in high yield of ethylene and propylene. Light olefin production via catalytic cracking of various industrial feedstocks, ranging from heavy hydrocarbons to ethane, over modified ZSM-5 zeolites, has been reviewed in the present paper. Furthermore, the influence of various employed promoters, i.e., alkali and alkaline earth, transition, rare earth elements, and phosphorus, on the chemical properties of the modified ZSM-5 and the performance of resulting catalyst in enhancing the selectivity to light olefins, have been addressed. Moreover, the influences of different factors, including the zeolite acidity, Si/Al ratio and the temperature, on the light olefin production and the reaction scheme have been specified. The role of incorporated element in the catalytic cracking mechanism is also summarized.

Enhanced visible light photocatalytic activity of novel polymeric g-C3N4 loaded with Ag nanoparticles

Abstract: Novel polymeric g-C3N4 photocatalysts loaded with noble metal Ag nanoparticles were prepared via a facile heating method. The obtained Ag/g-C3N4 composite products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectra (DRS) and photoluminescence spectra (PL). The photocatalytic activities of Ag/g-C3N4 samples were investigated based on the decomposition of methyl orange and hydrogen evolution under visible light irradiation. The XPS results revealed that it was the metallic Ag0 deposited on polymeric g-C3N4 samples. The Ag/g-C3N4 photocatalysts exhibited significantly enhanced photocatalytic performance for the degradation of methyl orange and hydrogen production compared with pure g-C3N4. The optimal Ag content was determined to be 1.0 wt%, and the corresponding hydrogen evolution rate was 10.105 μmol h−1, which exceeded that of pure g-C3N4 by more than 11.7 times. The enhanced photocatalytic performance could be attributed to the synergic effect between Ag and g-C3N4, which promoted the migration efficiency of photo-generated carriers. The proposed mechanism for the enhanced visible light photocatalytic activity of g-C3N4 modified by a small amount of Ag was further confirmed by photoluminescence spectroscopy.

Hydrodeoxygenation of guaiacol as model compound for pyrolysis oil on transition metal phosphide hydroprocessing catalysts

Abstract: The gas phase hydrodeoxygenation (HDO) of guaiacol, as a model compound for pyrolysis oil, was tested on a series of novel hydroprocessing catalysts – transition metal phosphides which included Ni2P/SiO2, Fe2P/SiO2, MoP/SiO2, Co2P/SiO2 and WP/SiO2. The turnover frequency based on active sites titrated by the chemisorption of CO followed the order: Ni2P > Co2P > Fe2P, WP, MoP. The major products from hydrodeoxygenation of guaiacol for the most active phosphides were benzene and phenol, with a small amount of methoxybenzene formed. Kinetic studies revealed the formation of reaction intermediates such as catechol and cresol at short contact times. A commercial catalyst 5% Pd/Al2O3 was more active than the metal phosphides at lower contact time but produced only catechol. A commercial CoMoS/Al2O3 deactivated quickly and showed little activity for the HDO of guaiacol at these conditions. Thus, transition metal phosphides are promising materials for catalytic HDO of biofuels.

Renewable fuels via catalytic hydrodeoxygenation

Abstract: There is considerable interest in investigating the deoxygenation process, due to the high oxygen content of the feed-stocks used for the production of renewable fuels This review addresses studies related to the catalytic hydrodeoxygenation of two feed-stocks (a) oils with high content of triglycerides and (b) oils derived from high pressure liquefaction or pyrolysis of biomass Future research directions that could potentially bridge the existing gaps in these areas are provided

XPS characterization of Au/TiO2 catalysts: Binding energy assessment and irradiation effects

Abstract: X-ray photoelectron spectroscopy (XPS) was employed to study the surface composition and electronic structure of Au/TiO2 catalysts in comparison with TiO2 (anatase) and to reveal time-dependent X-ray irradiation damage of the samples. The occurrence of Au nano-sized particles on a TiO2 support was found to result in a slight shift of Ti 2p core-level spectrum and in changes of the valence band and X-ray induced Auger spectra, compared to TiO2-only. It was shown that for different means of energy referencing the charge-corrected Au 4f7/2 binding energy in Au/TiO2 catalysts was 0.15–0.45 eV lower than that in pure bulk Au. Exposure to X-rays of Au/TiO2 catalysts and pure TiO2 caused a reduction of Ti 4+ oxidation state and desorption of oxygen from the surface. As a result, the surface chemical composition and electronic structure of the samples changed with time. The X-ray irradiation affected charge transfer processes in Au/TiO2 so that the pattern of X-ray induced damage in the Au-based catalyst turned out to be quite different from that in TiO2, with some characteristics displaying the very opposite features. Decreasing of the Au 4f7/2 binding energy and concurrent increasing of the fraction of Ti3+ species observed in the beginning of X-ray irradiation of Au/TiO2 may be taken as direct evidence for charge transfer from oxygen vacancies created by irradiation to Au particles.

Catalytic performance and characterization of Ni-Fe catalysts for the steam reforming of tar from biomass pyrolysis to synthesis gas

Abstract: Catalytic performance of Ni-Fe/Al2O3 catalysts with the optimum composition was much higher than corresponding monometallic Ni and Fe catalysts in the steam reforming of tar from the pyrolysis of cedar wood. According to the catalyst characterization, the Ni-Fe alloys were formed and the Fe atoms on the alloys tend to be enriched on the surface, and it was suggested that the structure was maintained mainly during the reaction. The surface Fe atoms supply oxygen species, enhancing the reaction of tar and suppressing the coke formation. Excess Fe addition decreased the catalytic activity by decreasing the surface Ni atoms.

Alcohols as alternative fuels: An overview

Abstract: Due to the phase out of lead in all gasoline grades and the adverse health and environmental effects of MTBE, the synthesis of higher alcohols, particularly ethanol, from synthesis gas has drawn considerable interest. Low molecular weight alcohols such as ethanol have replaced other additives as octane boosters in automotive fuels. Adding alcohols to petroleum products allows the fuel to combust more completely due to the presence of oxygen, which increases the combustion efficiency and reduces air pollution. The presence of alcohols in fuel causes corrosion to metallic fuel system components. In order to make the best use of alcohols as alternative fuels; one can redesign the engine or the vehicle can be redesign or one can blend in one or more additives to the ethanol or methanol to improve its characteristics. Catalytic conversion of synthesis gas to alcohols is advantageous, as this uses various renewable and non-renewable carbon resources. Different catalytic systems can be used for synthesizing higher alcohols from synthesis gas. Depending on the process conditions and the catalyst used, the reaction mechanism varies and the products include primary and secondary alcohols of both normal and branched carbon chains. The present paper includes an overview of the processes and catalysts used depending on the production of specific alcohols, as well as, the reaction mechanisms currently accepted. Transition metal-promoted alkali-modified molybdenum sulphide catalysts are considered to be more attractive to improve CO hydrogenation and for the production of linear alcohols.

Methane reforming to synthesis gas over Ni catalysts modified with noble metals

Abstract: Nickel is an effective component for the steam reforming of methane in terms of the catalytic activity and the catalyst cost. When Ni catalysts are applied to dry reforming, oxidative reforming, and catalytic partial oxidation, it is necessary to add the properties of high resistance to oxidation, hot spot formation, and coke deposition, to the Ni catalysts. An efficient method for giving these properties while considering the catalyst cost is the modification of Ni metal particles with small amounts of noble metals. An important point is that preparation methods can affect the structure of noble metal–Ni bimetallic particles, which is connected to the catalytic performances. The additive effects of noble metals on the catalytic performances are summarized in terms of activity, suppression of Ni oxidation, carbon formation, self-activation, and sustainability in the daily startup and shutdown operations.

C–N–S tridoped TiO2 for photocatalytic degradation of tetracycline under visible-light irradiation

Abstract: C–N–S tridoped TiO2 was synthesized using a facile, cost-effective and easily scaled-up sol–gel method with titanium butoxide (Ti(OC4H9)4) as titanium precursor and thiourea as the dopant source. It was found that thiourea could suppress the crystal growth of the anatase TiO2 and inhibit its transformation from anatase to rutile phase. X-ray photoelectron spectroscopy (XPS) analysis revealed that carbon substituted some of the oxygen to form Ti–C bonds, nitrogen was interstitially and substitutionally doped into the TiO2 lattices to form Ti–N–O, Ti–O–N and O–Ti–N, and S6+ substituted for the lattice Ti4+ to result in cationic sulfur doping. The photocatalyst with the thiourea-to-Ti molar ratio of 0.05:1 and calcined at 450 °C (T0.05–450) possessed the optimum surface elemental contents of C (12.56 at.%, excluded adventitious carbon at 284.8 eV), N (0.54 at.%) and S (1.60 at.%) based on the XPS analysis, and exhibited the highest photocatalytic degradation efficiency of tetracycline (TC) under visible-light irradiation. This was attributed to the synergistic effects of TC adsorption on T0.05–450 due to its high specific surface area, band gap narrowing resulting from C–N–S tridoping, presence of carbonaceous species serving as photosensitizer, and well-formed anatase phase. The slightly alkaline pH condition and solar irradiation were more favorable for both the photocatalytic degradation and mineralization of TC. Microtox assay indicated that the extended solar photocatalysis was efficient in the detoxification of TC solution.

Effect of Ce/Zr composition and noble metal promotion on nickel based CexZr1−xO2 catalysts for carbon dioxide methanation

Abstract: Carbon dioxide methanation was carried out over a series of Ni-CexZr1-xO2 catalysts prepared by a pseudo sol-gel method. The influence of CeO2/ZrO2 mass ratio and noble metal addition was investigated. The catalysts were subsequently characterized by means of XRD,TPR, BET, H-2-TPD and SEM-EDX. The modification of structural and redox properties of these materials was evaluated in relation with their catalytic performances. All catalysts gave impressive CO2 conversion and extremely high selectivity to methane (superior to 98%). Ni2+ incorporation into the CZ structure was proved to enhance catalysts specific activity. The global performance of the studied systems depended not only on the surface of available metallic nickel but also on the composition of the support and on its modification by Ni2+ doping. As a result of these two phenomena, the Ni-based mixed oxide having a CeO2/ZrO2 = 60/40 exhibited the highest catalytic activity, owing to an optimal Ni2+/Ni-0 ratio. Noble metal addition led to higher Ni dispersion, resulting in a raise of both activity and catalyst life-time. It did not modify the support intrinsic activity. The deactivation was shown not to be due to carbon deposits but rather to nickel particles sintering. The investigated parameters thus allowed an improvement of the previously studied 5 wt% Ni-Ce0.72Zr0.28O2 system. (C) 2010 Elsevier B.V. All rights reserved.

Visible light responsive iodine-doped TiO2 for photocatalytic reduction of CO2 to fuels

Abstract: Iodine-doped titanium oxide (I-TiO2) nanoparticles that are photocatalitically responsive to visible light illumination have been synthesized by hydrothermal method. The structure and properties of I-TiO2 nanocrystals prepared with different iodine doping levels and/or calcination temperatures were characterized by X-ray diffraction, transmission electron microscopy and diffraction, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The three nominal iodine dopant levels (5, 10, 15 wt.%) and the two lower calcination temperatures (375, 450 °C) produced mixture of anatase and brookite nanocrystals, with small fraction of rutile found at 550 °C. The anatase phase of TiO2 increased in volume fraction with increased calcination temperature and iodine levels. The photocatalytic activities of the I-TiO2 powders were investigated by photocatalytic reduction of CO2 with H2O under visible light (λ > 400 nm) and also under UV–vis illumination. CO was found to be the major photoreduction product using both undoped and doped TiO2. A high CO2 reduction activity was observed for I-TiO2 catalysts (highest CO yield equivalent to 2.4 μmol g−1 h−1) under visible light, and they also had much higher CO2 photoreduction efficiency than undoped TiO2 under UV–vis irradiation. I-TiO2 calcined at 375 °C has superior activity to those calcined at higher temperatures. Optimal doping levels of iodine were identified under visible and UV–vis irradiations, respectively. This is the first study that investigates nonmetal doped TiO2 without other co-catalysts for CO2 photoreduction to fuels under visible light.

Nano ZnO synthesis by modified sol gel method and its application in heterogeneous photocatalytic removal of phenol from water

Abstract: Zinc oxide nanoparticles were synthesized by precipitation and modified sol gel methods. The influence of calcination temperature on morphology and crystallite size of ZnO was studied by varying temperature from 400 to 700 °C. The nano-structured ZnO particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDXS) and tranmission electron microscopy (TEM). The photo catalytic activity of as-prepared ZnO was evaluated by degradation of phenol under UV laser irradiation. The Photocatalytic degradation (PCD) efficiency of ZnO was found to decrease with the increase in calcination temperature due to agglomeration of particles and the increase in particle size. In addition to the effect of calcination temperature, the influence of various other parameters such as photocatalyst concentration, initial pH and the initial phenol concentration was also investigated to achieve the maximum PCD of phenol. The operational parameters show the expected influence regarding the efficiency of the photocatalytic degradation process. The results follow the pseudo-first order rate kinetics.

Sulfamic acid-functionalized magnetic Fe3O4 nanoparticles as an efficient and reusable catalyst for one-pot synthesis of α-amino nitriles in water

Abstract: Grafting of chlorosulfuric acid on the amino-functionalized Fe3O4 nanoparticles afforded sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-MNPs) as a novel organic–inorganic hybrid heterogeneous catalyst, which was characterized by XRD, FT-IR, TGA, TEM, and elemental analysis. The catalytic activity of SA-MNPs was probed through one-pot synthesis of α-amino nitriles via three-component couplings of aldehydes (or ketones), amines and trimethylsilyl cyanide in water, at room temperature. The heterogeneous catalyst could be recovered easily and reused many times without significant loss of its catalytic activity.

Deactivation of HDS catalysts in deoxygenation of vegetable oils

Abstract: Several rapeseed oils with different degree of upgrading were used as feedstocks for deoxygenation over sulfided CoMo/γ-Al 2 O 3 catalyst. The rapeseed oil samples differed in the concentration of inorganic impurities, water, free fatty acids and phospholipids. The catalytic experiments were carried out in a fixed bed reactor at constant reaction conditions (310 °C, WHSV = 2 h −1 , hydrogen pressure 3.5 MPa). Refined rapeseed oils were converted to hydrocarbons more efficiently than neat rapeseed oil, trap grease and waste oil. The high concentration of phospholipids in trap grease was the most likely cause of catalyst deactivation by coking. Decomposition of phospholipids as well as oligomerization of rapeseed oil by phosphoric acid at 310 °C was confirmed by separate laboratory experiments. The high concentration of alkalis in waste rapeseed oil was the main reason for increased deactivation in comparison with neat rapeseed oil. Sulfur removal from catalyst active sites affected adversely the deoxygenation of triglycerides. The catalyst deoxygenation activity was partially restored by pulse addition of dimethyldisulfide (DMDS) to the feedstock, however the degradation of active sites by loss of sulfur was not fully reversible. In contrast, continually added sulfur agent (DMDS) ensured significantly slower catalyst deactivation. Moreover, presence of H 2 S lowered considerably hydrodeoxygenation/decarboxylation ratio.

Rapid synthesis of 1-amidoalkyl-2-naphthols over sulfonic acid functionalized imidazolium salts

Abstract: Novel sulfonic acid functionalized imidazolium salts including 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl} (an ionic liquid), 1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} (an ionic liquid) and 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate {[Msim]AlCl4} (a solid) efficiently catalyze one-pot multi-component condensation of β-naphthol with aromatic aldehydes and amide derivatives under solvent-free conditions to afford 1-amidoalkyl-2-naphthols in excellent yields (81–96%) and in very short reaction times (1–40 min).

Hydrogenolysis of glycerol on bimetallic Pd-Cu/solid-base catalysts prepared via layered double hydroxides precursors

Abstract: A series of bimetallic Pd-Cu/solid-base catalysts were prepared via thermal decomposition of Pd x Cu 0.4 Mg 5.6− x Al 2 (OH) 16 CO 3 layered double hydroxides precursors and used in hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). X-ray diffraction (XRD), scanning electron microscopy (SEM) and N 2 O oxidation and followed H 2 titration characterizations confirmed that well structured layered double hydroxides Pd x Cu 0.4 Mg 5.6− x Al 2 (OH) 16 CO 3 crystals could be prepared when the amount of added Pd was less than x x Cu 0.4 /Mg 5.6− x Al 2 O 8.6− x and Pd improved the reduction of Cu. Hydrogenolysis of glycerol proceeded easily on bimetallic Pd-Cu/solid-base catalysts than separated Pd and Cu. On Pd 0.04 Cu 0.4 /Mg 5.56 Al 2 O 8.56 , the conversion of glycerol and selectivity of 1,2-PDO reached 88.0 and 99.6%, respectively, at 2.0 MPa H 2 , 180 °C, 10 h in ethanol solution. And this catalyst is stable in five recycles. It was concluded that H 2 -spillover from Pd to Cu increased the activity of Pd x Cu 0.4 /Mg 5.6− x Al 2 O 8.6− x in hydrogenolysis of glycerol.

Solid acid catalyzed glucose conversion to ethyl levulinate

Abstract: A series of solid acid catalysts including SO 4 2− /ZrO 2 , SO 4 2− /TiO 2 , SO 4 2− /ZrO 2 –TiO 2 and SO 4 2− /ZrO 2 –Al 2 O 3 were prepared by precipitation and impregnation method for ethyl levulinate production from glucose in ethanol. Effects of various reaction parameters and catalyst reuse cycle towards the reaction performance were studied. Experimental results showed that different components of the sulfated metal oxides had markedly different catalytic effects on the ethanolysis of glucose. SO 4 2− /ZrO 2 –Al 2 O 3 could significantly suppress the formation of ethyl levulinate due to the incorporation of Al 2 O 3 . With SO 4 2− /ZrO 2 as the catalyst, an optimized ethyl levulinate yield of above 30 mol% was obtained at 200 °C for 3 h with catalyst dosage of 2.5 wt%, and the recovered catalyst after calcination was found to remain active with an almost unchanged product yield after being reused five times. The main liquid substances including ethyl levulinate, diethyl ether and ethanol can be easily separated from the resulting product mixture by fractionation and the excess ethanol was recycled. The physicochemical properties of the prepared and thermally regenerated catalysts were characterized using BET surface area, XRD, NH 3 -TPD and XPS techniques.

12-Tungstophosphoric acid anchored to SBA-15: An efficient, environmentally benign reusable catalysts for biodiesel production by esterification of free fatty acids

Abstract: 12-Tungstophosphoric acid anchored to SBA-15 was synthesized and characterized by various physico-chemical techniques such as TGA, FT-IR, DRS, XRD, N 2 adsorption–desorption, solid state NMR ( 31 P and 29 Si), SEM and TEM. The use of synthesized catalyst was explored for biodiesel production by esterification of free fatty acid, oleic acid with methanol. Influence of various reaction parameters (such as catalyst concentration, acid/alcohol molar ratio and reaction temperature) on catalytic performance was studied. The catalyst shows high activity in terms of conversion of oleic acid as well as high turnover frequency of 9.3 min −1 . It also shows potential of being used as recyclable catalyst material after simple regeneration. Kinetic investigation reveals that the esterification reaction of oleic acid with methanol follows a first order dependency on the concentration of the oleic acid and the catalyst. The influence of temperature on rate constant was also studied and the activation energy was found to be 44.6 kJ mol −1 . As an application, preliminary study was carried out for biodiesel production from waste cooking oil, as feedstock without any pre-treatment, with methanol. Studies show that the catalyst can be used for biodiesel production from waste cooking oil under mild conditions.

A new approach in the evaluation of the support effect for NiMo hydrodesulfurization catalysts

Abstract: To evaluate the intrinsic effect of some supports (γ-Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 ) on the activity of hydrodesulfurization (HDS) catalysts, NiMo catalysts were prepared by adding nickel acetylacetonate (Ni(acac) 2 ) to supported molybdenum sulfide. The catalysts were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy and then tested in HDS of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT). This preparation method allowed obtaining well-promoted catalysts. A higher percentage (69–80%) of NiMoS phase was observed by XPS for these catalysts than for traditional co-impregnated catalysts (60%). In addition, the catalytic activity measured with those promoted systems was improved especially for TiO 2 and ZrO 2 supported NiMoS catalysts. By combining characterizations, geometrical model and catalytic activities, apparent HDS activities per NiMoS site were evaluated on each support. The high quality of NiMoS sites suggests that Type-II sites have been formed on silica.

Silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO): A highly efficient, reusable and new heterogeneous catalyst for the synthesis of 4H-benzo[b]pyran derivatives

Abstract: The reaction of 3-chloropropyl silica with diazabicyclo[2.2.2]octane in dry acetone affords silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO) as a new basic catalyst. The catalyst is used for the efficient synthesis of 4H-benzo[b]pyran derivatives via one-pot three-component reaction of cyclic ketones/1,3-diketones with aromatic aldehydes and alkylmalonates.

CaO-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate: Isolation and characterization of an active Ca species

Abstract: The transesterification of dimethyl carbonate (DMC) with glycerol to produce glycerol carbonate was investigated in the presence of CaO under various reaction conditions. CaO was completely dissolved in the reaction mixture of glycerol and DMC in 5 min at 75 °C and at the molar ratio of glycerol/DMC/CaO of 1/2/0.01. The isolation and the characterization of the dissolved Ca species by means of TOF-SIMS, elemental analysis, and FT-IR revealed that an active species, Ca(C 3 H 7 O 3 )(OCO 2 CH 3 ) is generated from the interaction of CaO with glycerol and DMC. The mechanistic pathways to the formations of Ca(C 3 H 7 O 3 )(OCO 2 CH 3 ) and glycerol carbonate are discussed on the basis of experimental and spectroscopic results.

Selective synthesis of 1-butanol from ethanol over strontium phosphate hydroxyapatite catalysts

Abstract: We previously reported the ability of strontium hydroxyapatite to catalyze the conversion of ethanol into 1-butanol with higher selectivity than that reported for calcium hydroxyapatite catalysts. In the present study, we investigated the catalytic conversions of ethanol over substituted hydroxyapatites, such as Sr 10 (PO 4 ) 6 (OH) 2 , Ca 10 (VO 4 ) 6 (OH) 2 , Sr 10 (VO 4 ) 6 (OH) 2 , and Ca 10 (PO 4 ) 6 (OH) 2 , and their solid solutions, such as Ca 10 − z Sr z (PO 4 ) 6 (OH) 2 , Ca 10 (PO 4 ) 6 − x (VO 4 ) 6 − x (OH) 2 , and Sr 10 (PO 4 ) 6 − x (VO 4 ) 6 − x (OH) 2 , were investigated. The strontium phosphate hydroxyapatite [Sr 10 (PO 4 ) 6 (OH) 2 : Sr–P] exhibited the highest 1-butanol selectivity among the tested catalysts in the region of the ethanol conversions between 1 and 24%. The reaction mechanism of 1-butanol formation over the Sr–P hydroxyapatite catalyst includes the dehydrogenation of ethanol into acetaldehyde, the aldol condensation of acetaldehyde into crotonaldehyde, and the hydrogenations of crotonaldehyde, 2-buten-1-ol, and/or butyraldehyde into 1-butanol. The Sr–P hydroxyapatite catalyst showed high selectivity into crotonaldehyde in the aldol condensation of acetaldehyde and inhibited the coking in the hydrogen transfer reaction of 2-buten-1-ol into 1-butanol, which might be reasons why the Sr–P hydroxyapatite catalyst showed the high 1-butanol selectivity in the catalytic conversion of ethanol.

Liquid phase aldol condensation reactions with MgO-ZrO2 and shape-selective nitrogen-substituted NaY

Abstract: The aldol condensation reactions of furfural/hydroxymethylfurfural (furfurals) with acetone/propanal in water–methanol solvents were studied over the solid base catalysts MgO–ZrO 2 , NaY and nitrogen-substituted NaY (Nit-NaY). The reactions were conducted at 120 °C and 750 psig of He in batch reactors. Nit-NaY exhibited catalytic activity for aldol condensation comparable to MgO–ZrO 2 and much higher than that of NaY, indicative of the increased base strength after replacing the bridging oxygen with the lower electronegativity nitrogen over Nit-NaY. The aldol condensation of furfurals with acetone produces two different products, the monomer and the dimer. The monomer is formed from reaction of furfurals with acetone. The dimer is formed from reaction of the monomer with furfurals. MgO–ZrO 2 had a higher selectivity towards dimer formation. In contrast, Nit-NaY was more selective towards the monomer product due to the cage size in the FAU structure, indicating that Nit-NaY is a shape selective base catalyst. Increasing the water concentration in the feed solution or increasing the feed concentration led to both increased catalytic activity and dimer selectivity. The Nit-NaY catalyst was not stable and lost catalytic activity when recycled due to leaching of the framework nitrogen. Different characterization techniques, including XRD, high resolution Ar adsorption isotherm, basic sites titration, CO 2 TPD-MS, TGA and 29 Si SP MAS NMR, were used here to characterize the fresh and spent catalysts. The results show that Nit-NaY maintains only part of the FAU-type crystal structure. Furthermore, the base strength over Nit-NaY was found to be between that of Mg 2+ –O 2− pair and Mg(OH) 2 . The reaction mechanism over Nit-NaY was discussed.

Synthesis of glycerol carbonate by transesterification of glycerol with dimethyl carbonate over Mg/Al/Zr catalysts

Abstract: Glycerol carbonate was synthesized by transesterification of glycerol with dimethyl carbonate using Mg/Al/Zr mixed oxide base catalysts. A series of Mg/Al/Zr catalysts were prepared with different molar ratios by using co-precipitation method and calcining at different temperatures. The catalysts were characterized by FT-infrared spectroscopy, X-ray diffraction and temperature-programmed desorption of CO2. The transesterification activity depends on the Mg/Al/Zr molar ratio and the catalyst with Mg/Al/Zr molar ratio of 3:1:1 showed excellent activity. The catalyst activity depends on the pretreatment temperature, structure and basicity of the catalysts. The transesterification activity of catalysts was correlated with the structural aspects and the amount of basicity. Various parameters such as reaction temperature, catalyst concentration and molar ratio of dimethyl carbonate to glycerol were studied to optimize the reaction conditions.

A comparative study for gas-phase dehydration of glycerol over H-zeolites

Abstract: The gas-phase dehydration of glycerol was conducted over various H-zeolites, viz. H-ferrierite, H-β, H-ZSM-5, H-Y and H-mordenite with various SiO 2 /Al 2 O 3 ratios. For comparison, γ-Al 2 O 3 and silica-alumina were also examined. Several characterization techniques: X-ray diffraction (XRD), the temperature-programmed desorption of ammonia (NH 3 -TPD), the temperature-programmed desorption of water (H 2 O-TPD), temperature-programmed oxidation (TPO) with mass spectroscopy and CHNS analysis were employed to characterize the catalysts. The initial glycerol conversion at 315 °C decreased in the following order: silica-alumina > H-β (25) > H-β (27) > γ-Al 2 O 3 > H-mordenite (20) > H-ferrierite (55) > H-ferrierite (20) > H-ZSM-5 (23) ∼ H-β (350) > H-β (38) ∼ H-Y (5.1). H-ferrierite (55) showed the highest selectivity to acrolein at 315 °C among the tested catalysts. The glycerol conversion over the solid acid catalysts was strongly dependent on their external surface area. In the case of the H-zeolites, most of the micropores were filled with carbon sources at the initial stage of this reaction. As long as the molar ratio between water and glycerol was in the range from 2 to 11, there was only a small change in the glycerol conversion, while the acrolein selectivity increased noticeably with increasing water content in the feed. The glycerol conversion and acrolein selectivity increased with increasing reaction temperature from 290 °C to 340 °C over H-ferrierite (55). The glycerol conversion and acrolein selectivity also increased with increasing contact time ( W / F glycerol ) which is defined as the ratio between the catalyst's weight ( W ) and the molar flow rate of glycerol ( F glycerol ).

Hydrotreatment of wood-based pyrolysis oil using zirconia-supported mono- and bimetallic (Pt, Pd, Rh) catalysts

Abstract: Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 °C, 20 MPa total pressure, and 4 h reaction time) with mono- and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO2 showed the highest activity, followed by Rh/ZrO2. Upgraded oils with the best product properties were obtained with Rh/ZrO2. For this catalyst, the TGA residue, which is a measure for coking tendency, was 13.4 wt% and the Mw of the upgraded oil (748 g/mol) was lowest. All noble metal catalysts showed higher activities per gram of metal than the benchmark catalyst CoMo/Al2O3. Hydrotreatment reactions at variable batch times were performed to gain insights in reaction pathways and showed the involvement of competitive hydrogenation/hydrocracking and polymerisation pathways. Temperature programmed oxidation (TPO) measurements of spent catalysts showed the presence of carbonaceous deposits on the catalyst (2–6 wt%). These deposits may be removed by oxidation at temperatures lower than 600 °C without changing the morphology of the catalyst.

Photocatalytic behavior of ZnO and Pt-incorporated ZnO nanoparticles in phenol degradation

Abstract: Nanostructured Pt–ZnO composite thick films were prepared using the composite nanoparticles synthesized through Triton X-100 polymer assisted thermolysis of zinc acetate. It has been observed that only a fraction of added Pt incorporates into the ZnO lattice and the rest segregates over the ZnO nanoparticle surface to form metallic nanoclusters. Morphology, crystallinity, and optical properties of the ZnO and Pt–ZnO nanostructures have been studied. Photocatalytic behavior of the samples for phenol degradation process has been studied in a high performance liquid chromatography system. It has been observed that though the phenol degradation rate is higher for pure ZnO nanostructures, Pt–ZnO nanostructures act as selective catalyst, producing only one intermediate product and dissociating it faster than ZnO.

Solvent effect in the liquid-phase hydrogenation of acetophenone over Ni/SiO2: A comprehensive study of the phenomenon

Abstract: The solvent effect on catalyst activity and selectivity for the liquid-phase hydrogenation of acetophenone (AP) to 1-phenylethanol was thoroughly investigated over Ni/SiO2. Solvents of different nature were used: protic (C1–C3 primary and secondary alcohols), aprotic polar (tetrahydrofuran, γ-butyrolactone, and acetonitrile) and apolar solvents (cyclohexane, toluene, and benzene). The solvent had a strong influence on the AP hydrogenation rate but did not modify significantly the selectivity to 1-phenylethanol that was always higher than 92%. The AP hydrogenation activity followed the order: C2–C3 alcohols > cyclohexane > toluene > tetrahydrofuran > γ-butyrolactone > methanol ≫ benzene ≅ acetonitrile. In order to explain this activity pattern, the solvent–AP, solvent–H2 and solvent–catalyst interactions were analyzed. For the analysis of the solvent–AP interactions in liquid phase, both classical measures of polarity and others based on different solvatochromic scales were considered. The H2 availability in the liquid phase was estimated from the H2 solubility at reaction conditions. Solvent–catalyst interactions were characterized by means of the adsorption enthalpies measured calorimetrically. A reasonable correlation between the catalyst activity and some solvatochromic parameters was found only when solvents of similar nature were compared. For protic solvents, the AP hydrogenation rate decreased with the solvent polarity and its ability for H-bond formation with AP. Instead, the solvent–AP interactions were weak when using apolar solvents and thereby the activity pattern was essentially determined by the strength of solvent–catalyst interactions. In the case of aprotic polar solvents, both the solvent–AP interactions in the liquid phase and the solvent adsorption strength on the catalyst surface influenced the hydrogenation activity. The highest catalytic activities were obtained when using C2–C3 alcohol solvents. These protic solvents adsorbed dissociatively on metal nickel surface increasing the number of active H available for the hydrogenation reaction; this effect was much more important in the case of 2-propanol.

Toluene hydrogenation at low temperature using a molybdenum carbide catalyst

Abstract: A molybdenum carbide catalyst prepared with a novel methodology and its toluene hydrogenation activity tested at temperatures within 423–598 K and 2.76 MPa is here reported. Almost 100% hydrogenation was achieved at 473 K with this catalyst. The activation energy was 58.1 kJ/mol with a zero-order reaction for toluene concentration, illustrating a behavior comparable to that of noble metals. Additional catalyst formulations were tested and their activities compared between them. XRD and Raman characterization of the catalysts allowed identification of several species in the newly synthesized catalyst, namely fcc-Mo 2 C and MoO 2 .