Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine

Co-precipitation, impregnation and ultrasonic sol–gel (USG) methods have been used to prepare Cu–Cr–Fe/γ-Al₂O₃ catalysts, which were further used to synthesize 2-methylpiperazine. The catalysts were characterized by XRD, XPS, TG/DSC, BET, TPR, AAS and TEM. It is found that preparation method can greatly impact the catalytic performance of the catalysts, the Cu–Cr–Fe/γ-Al₂O₃ catalyst prepared by the ultrasonic sol–gel method proved to be the most active and stable for this reaction. The dispersion and stabilization of Cu⁰ in the reduced catalysts are attributed to the existence of CuCr₂O₄ and Fe₂O₃. A surprising copper migration was detected by XPS analysis for the Cu–Cr–Fe/γ-Al₂O₃-USG catalyst after the calcination process, which may be crucial to the high activity and stability of this catalyst.     

Selective hydrogenation of maleic anhydride to γ-butyrolactone and tetrahydrofuran by Cu–Zn–Zr catalyst in the presence of ethanol

A series of Cu–Zn–Zr catalysts were prepared by a coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N₂ adsorption. The catalytic activity of the Cu–Zn–Zr catalyst in the hydrogenation of maleic anhydride using ethanol as a solvent was studied at 220–280 °C and 1 MPa. Maleic anhydride was mainly hydrogenated to γ-butyrolactone and tetrahydrofuran while ethanol dehydrogenated to ethyl acetate. After reduction, CuO species present in the calcined Cu–Zn–Zr catalysts were converted to metallic copper (Cu⁰). The presence of ZrO₂ favored the deep hydrogenation of γ-butyrolactone to tetrahydrofuran while the presence of ZnO was beneficial to the formation of the intermediate product γ-butyrolactone. The molar ratios of the hydrogen produced in ethanol dehydrogenation to the hydrogen consumed in maleic anhydride hydrogenation increased with the increase of the reaction temperature.     

A Comparison of Oxygen-vacancy Effect on Activity Behaviors of Carbon Dioxide and Steam Reforming of Methane over Supported Nickel Catalysts

Partial oxidative steaming reforming of methanol (POSRM) to produce hydrogen selectively for polymer electrolyte membrane fuel cell (PEMFC) powering vehicles was studied over Cu–ZnO/samaria-doped ceria (SDC) catalyst. Compared with Cu–ZnO/α-Al₂O₃ and Cu–ZnO/γ-Al₂O₃ catalysts, the Cu–ZnO/SDC catalyst exhibited higher activity for CH₃OH conversion and higher selectivity for H₂ production in the POSRM reaction. The higher catalytic performance of Cu–ZnO/SDC appears attributable to the support effect of SDC. Effects of reaction temperature, O₂/CH₃OH and H₂O/CH₃OH molar ratios on the catalytic performance of Cu–ZnO/SDC were investigated. It has been found that the partial-oxidation nature of the POSRM reaction is increased when O₂/CH₃OH ratio is increased, and the combustion of methanol and H₂ would occur insignificantly in the POSRM over the Cu–ZnO/SDC catalyst. A higher concentration of steam is beneficial to suppress CO formation over the Cu–ZnO/SDC catalyst. Under the experimental conditions of the present work, the O₂/CH₃OH and H₂O/CH₃OH molar ratios should be about 0.02 and 1.0–2.0, respectively, in order for Cu–ZnO/SDC to achieve an optimum catalytic performance.     

Dehydrogenation of cyclohexanol on Cu–ZnO/SiO2 catalysts: The role of copper species

For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO₂ catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H₂–N₂O titration, BET, H₂-TPR, NH₃-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO₂ (CZS) catalysts. Cu⁰ and Cu⁺ species were found on the reduced CZS catalysts surface, and the amount of Cu⁺ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu⁰ species can be found on the reduced Cu/SiO₂ (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu⁺ species, the Cu⁺ species should be the active sites for the production of phenol, the Cu⁰ is responsible for cyclohexanol dehydrogenation to cyclohexanone.     

On the Limited Selectivity of Silica-Based Epoxidation Catalysts

Epoxidation of 2-cyclohexen-1-ol with TBHP and TiO₂–SiO₂, Fe₂O₃–SiO₂ and SiO₂ aerogels has been studied. The influence of surface silanol groups and transition metal impurities in titania–silica on the product distribution has been analyzed. The results, supported by literature data, indicate that high surface area silica cannot generally be regarded as an inert matrix in epoxidation catalysts. Contribution of Ti-free silica limits the selectivity of Ti- and Si-containing catalysts in demanding epoxidation reactions. The activity of silica – together with the background oxidation of the olefin – may lead to overestimated intrinsic activities when the reaction rate is related to the Ti content of the catalyst.     

Enantioselectivity promotion by achiral surface functionalization on SiO2-supported Cu-bis(oxazoline) catalysts for asymmetric Diels–Alder reactions

Novel SiO₂-supported chiral Cu-bis(oxazoline) (BOX) complexes for asymmetric Diels–Alder reactions were prepared by combining metal-complex immobilization with surface functionalization using achiral silane-coupling reagents on SiO₂. We found that the surface functionalization of a SiO₂-supported Cu-BOX catalyst with achiral 3-methacryloxypropyltrimethoxysilane dramatically increased enantioselectivity in the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. The Cu-BOX complexes on bare and functionalized SiO₂ surfaces were characterized by XAFS, ESR, FT-IR, UV/vis, and ²⁹Si solid-state MAS NMR. The large increase in enantioselectivity by achiral surface species without chiral center may be due to a glue effect, creating a new chiral ensemble structure at the surface.     

Preparation and characterization of silica-supported, group IB–Pd bimetallic catalysts prepared by electroless deposition methods

Electroless deposition has been used to synthesize a series of Au–, Ag–, and Cu–Pd/SiO₂ bimetallic catalysts having incremental surface coverages and compositions of each group IB metal. Thermodynamically unstable, yet kinetically stable, electroless bath(s) were developed using metal bis-cyano salts of the group 1B metal and N₂H₄ (for Au and Ag) or DMAB (for Cu) as reducing agents. The times (1–2 h) and profiles (1st order in group 1B metal concentration) observed for complete deposition indicate good kinetic control of the electroless deposition process. The bimetallic catalysts have been characterized using selective chemisorption, atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FTIR) of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) techniques. Decreases in Pd surface sites with addition of IB metals confirm deposition onto the supported Pd nanoparticle surfaces. FTIR studies suggest that deposition of Cu and Ag are selective towards Pd(1 1 1) sites, while Au deposits non-discriminately on all Pd sites. Finally, XPS measurements for each family of bimetallic catalysts suggest a net electron transfer from the Pd to the deposited metal.     

On the structure-sensitivity of 2-butanol dehydrogenation over Cu/SiO2 cogelled xerogel catalysts

Cu/SiO₂ cogelled xerogel catalysts were synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Cu with 3-(2-aminoethylamino)-propyltrimethoxysilane (EDAS). The resulting catalysts are composed of metallic crystallites with a diameter of about 3 nm located inside microporous silica particles and larger metallic particles with a diameter of 8–30 nm located outside silica network. Cu/SiO₂ catalysts were tested for 2-butanol dehydrogenation. This reaction over Cu/SiO₂ cogelled xerogel catalysts is a structure-sensitive reaction: large metallic particles located outside silica particles are responsible for the dehydrogenation reaction, while small metallic particles located inside silica particles do not participate to the reaction.     

Novel stereo controlled glycosylation of 1,2,3,4,6-penta-o-acetyl-β-d-glucopyranoside using MgO–ZrO2 as an environmentally benign catalyst

Glycosylation reactions are most commonly encountered in nature. Synthetically, glycosylations are carried out with Lewis acid catalysts or mineral acids. However an environmental threat associated with catalysts has encouraged process modification by alternative development of solid catalysts based glycosylation reactions, which are commercially viable as well. In this contribution comparative study of glycosidic bond formation of 1,2,3,4,6-penta-o-acetyl-β-d-glucopyranoside with various alcohols over variety of reaction promoters/catalyst like p-toluene sulphonic acid, HCl, H₂SO₄ and MgO–ZrO₂ were taken up to evaluate the performance of this potential promoter/catalysts systems. The best catalyst for the selective synthesis of alkyl-β-d-glucopyranosides was MgO–ZrO₂ which remains active upto three runs. This replacement of homogeneous acid catalysts by heterogeneous base catalyst shows alkyl-β-d-glucopyranoside as major product at comparatively low temperature range. The effects of variety of parameters were studied in a batch reactor. The mechanism of the reaction over basic mixed metal oxide at 363 K is put forth.     

The difference in the active sites for CO2 and CO hydrogenations on Cu/ZnO-based methanol synthesis catalysts

The effect of Zn in copper catalysts on the activities for both CO₂ and CO hydrogenations has been examined using a physical mixture of Cu/SiO₂+ZnO/SiO₂ and a Zn-containing Cu/SiO₂ catalyst or (Zn)Cu/SiO₂. Reduction of the physical mixture with H₂ at 573–723 K results in an increase in the yield of methanol produced by the CO₂ hydrogenation, while no such a promotion was observed for the CO hydrogenation, indicating that the active site is different for the CO₂ and CO hydrogenations. However, the methanol yield by CO hydrogenation is significantly increased by the oxidation treatment of the (Zn)Cu/SiO₂ catalyst. Thus it is concluded that the Cu–Zn site is active for the CO₂ hydrogenation as previously reported, while the Cu–O–Zn site is active for the CO hydrogenation.     

Changes in Physico-Chemical Properties of Iron-Based Fischer–Tropsch Catalyst Induced by SiO2 Addition

The effect of adding SiO₂ to a precipitated Fe-based Fischer–Tropsch catalyst was investigated. Silica was added to the catalyst either during or after precipitation. The iron-based Fischer–Tropsch catalysts were studied using Mössbauer spectroscopy, BET surface area, XRD and SEM characterization methods. Adding SiO₂ to the catalyst during precipitation or immediately after precipitation (i.e., precipitated SiO₂) results in the formation of Fe crystallites with an average diameter less than 3 nm, which have high surface areas and exhibit a strong interaction with the SiO₂ matrix. Consequently, these crystallites are resistant to reduction and carburisation. When SiO₂ was added to the catalyst after heat treatment (i.e., binder SiO₂), the resulting catalyst was observed to consist of segregated SiO₂-rich and Fe-rich phases. The distribution of K₂O in both these phases indicates that the amount of effective K₂O, i.e., that associated with Fe, is less when SiO₂ is added as a binder. The low extent of reduction and carburisation observed with catalysts that contain precipitated SiO₂ results in catalysts with low % CO conversion. A positive correlation between the amount of iron carbides present in the catalyst and the % CO conversion was observed in these studies.     

W-promoted Co–Mo–K/γ–Al2O3 catalysts for water–gas shift reaction

The effects of incorporating tungsten into the traditional Co–Mo–K/γ–Al₂O₃ catalysts on the catalytic performances for water–gas shift reaction were investigated. Activity tests showed that W-promoted Co–Mo–K/γ–Al₂O₃ catalysts exhibited higher activity than W-free Co–Mo–K/γ–Al₂O₃ catalyst. Raman and H₂-TPR studies indicated that part of the octahedrally coordinated Mo–O species on Co–Mo–K catalysts transformed into tetrahedrally coordinated Mo–O species in the presence of W promoter.     

Synthesis of proton conductive membranes based on inorganic–organic hybrid structure bound with phosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol–gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. ¹³C and ²⁹Si NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si–O–Si linkages by sol–gel reaction. TG–DTA analysis revealed that these membranes were thermally stable up to 200 °C in dry O₂. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA = 1/6 revealed proton conductivities of 6.3 × 10⁻³ and 2.4 × 10⁻⁴ S cm⁻¹ at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 °C.     

Preparation of alkali-resistant, Sil-1 encapsulated nickel catalysts for direct internal reforming-molten carbonate fuel cell

A thin layer of silicalite-1 zeolite membrane was grown on the surface of Ni/SiO₂ and Ni/Al₂O₃ catalyst beads after seeding and secondary regrowth to create core–shell catalysts that are resistant to alkali poisoning from direct internal reforming-molten carbonate fuel cell (DIR-MCFC). The zeolite shell thickness was optimized to prevent poisoning and minimize diffusion resistance. An out-of-cell test was designed to simulate the fuel cell operating conditions, which showed that the new core–shell catalysts maintained a high activity similar to the original fresh catalyst in spite of the exposure to alkali vapor at high temperature. The conventional Ni/SiO₂ and Ni/Al₂O₃ catalysts suffered higher than 80% decrease in activity for steam reforming of methane reaction (SRM).     

Effect of Ru addition to Co/SiO2/HZSM-5 catalysts on Fischer–Tropsch synthesis of gasoline-range hydrocarbons

Microporous HZSM-5 zeolite and mesoporous SiO₂ supported Ru–Co catalysts of various Ru adding amounts were prepared and evaluated for Fischer–Tropsch synthesis (FTS) of gasoline-range hydrocarbons (C₅–C₁₂). The tailor-made Ru–Co/SiO₂/HZSM-5 catalysts possessed both micro- and mesopores, which accelerated hydrocracking/hydroisomerization of long-chain products and provided quick mass transfer channels respectively during FTS. In the same time, Ru increased Co reduction degree by hydrogen spillover, thus CO conversion of 62.8% and gasoline-range hydrocarbon selectivity of 47%, including more than 14% isoparaffins, were achieved simultaneously when Ru content was optimized at 1 wt% in Ru–Co/SiO₂/HZSM-5 catalyst.     

Layered Double Hydroxides Containing Chiral Organic Guests: Synthesis, Characterization and Application for Asymmetric C–C Bond-Forming Reactions

We designed and developed two heterogeneous enantioselective catalysts, LDH-proline and LDH-BINOL, by incorporating chiral organic molecules viz., L-proline and S-BINOL, into layered double hydroxides (LDHs). These catalysts are characterized by IR, UV/vis and TGA analysis. These organo-LDHs have been successfully employed for various asymmetric C–C bond-forming transformations, and the products are obtained with good to excellent yields albeit low enantiomeric excess.     

Evidence of strong metal–oxide interactions in promoted Rh/SiO2 on CO hydrogenation: Analysis at the site level using SSITKA

It has been suggested that the behavior of Group VIII metal catalysts supported on transition metal oxides can be significantly affected by pretreatment conditions due to strong metal–oxide interactions (SMOI). However, the origins for the SMOI effect are still in debate. In this research, SMOI of Rh and vanadium oxide (as a promoter) supported on SiO₂ were studied at the site level for the first time, which provides an insight into the modification of surface properties after high temperature reduction. H₂ chemisorption, Fischer–Tropsch synthesis (FTS), and SSITKA (steady-state isotopic transient kinetic analysis) were used to probe the SMOI effects. The catalytic properties of the catalysts for CO hydrogenation were investigated using a differential fixed bed reactor at 230 °C and 1.8 atm, while for SSITKA, a reaction temperature of 280 °C and an excess of H₂ was used to maximize methane production. The addition of V to Rh/SiO₂ suppresses H₂ chemisorption, and high reduction temperature further decreases H₂ chemisorption on Rh/V/SiO₂ but has little effect on Rh/SiO₂. As reduction temperature increases, the activity for CO hydrogenation on Rh/SiO₂ remains essentially unchanged, but the activity of Rh/V/SiO₂ decreases significantly. SSITKA shows that the concentration of surface reaction intermediates decreases on Rh/V/SiO₂ as the reduction temperature increases, but the activities of the reaction sites increase. The results suggest that Rh being covered by VO_x species is probably the main reason for the decreased overall activity induced by high reduction temperature, but more active sites appear to be formed probably at the Rh–VO_x interface.     

Sb-V-Ox catalysts—Role of chemical composition of MCM-41 supports in physicochemical properties

SbVO_x binary oxides were loaded on MCM-41 matrices of various chemical compositions: silicate (MCM-41), Nb-silicate (NbMCM-41), and Al-silicate (AlMCM-41). Vanadium and antimony were introduced by the post synthesis wetness impregnation carried out step by step (first V next Sb). The materials were characterised by N₂ adsorption/desorption, XRD, UV–vis, ESR, H₂-TPR, FT-IR combined with pyridine adsorption, and test reaction–hydrosulphurisation of methanol. SbVO_x dispersion was much higher when the support contained transition metal (NbMCM-41). Tetrahedrally coordinated vanadium(IV) species were deduced on all prepared samples from UV–vis spectra and were the only registered species on SbV/NbMCM-41 and SbV/AlMCM-41, whereas octahedrally ones were also present on SbV/MCM-41 and SbV/SiO₂. In bulk SbVO_x octahedral coordination dominated. The chemical composition of mesoporous support determined acidic–basic properties of SbVO_x catalysts and influenced the activity and selectivity in methanol hydrosulphurisation. The presence of Lewis acid–base pairs in the SbV/AlMCM-41 and SbV/NbMCM-41 catalysts strongly activated thiol formation in the reaction between methanol and hydrogen sulphide, whereas bulk binary oxides and SbVO_x loaded on silicate MCM-41 were less active and exhibited different selectivity.     

Study on products distribution of iron and iron–zeolite catalysts in Fischer–Tropsch synthesis

The dependencies of hydrocarbon product distributions of iron and physical mixture of iron–zeolite catalyzed Fischer–Tropsch synthesis on reaction conditions include: reaction temperature, reaction pressure, H₂/CO feed ratios; space velocity and effect of zeolite presence have been investigated. The concept of two superimposed Anderson–Schulz–Flory distributions has been applied for the representation of the product distribution for both iron and iron–zeolite catalysts. Zeolite presence increased secondary reactions that include cracking of heavier products and light olefins oligomerization. Product distribution of iron–zeolite catalyst was comparable with iron catalyst at high space velocity, because the role of the zeolite on overall reaction declined.The results of the product distribution dependency on the reaction conditions over both iron and iron–zeolite catalysts showed that the average number of carbon decreases with H₂/CO ratio increasing and the reaction temperature in product.