Studies on the synthesis of higher alcohol over modified Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Higher alcohol has been considered as a potential fuel additive. Higher alcohol, including C₂–C₄ alcohol was synthesized by catalytic conversion of syngas (with a ratio of CO/H₂?=?1) derived from natural gas over modified Cu/ZnO/Al₂O₃ catalyst. Modified Cu/ZnO/Al₂O₃ catalysts promoted by alkali metal (Li) for higher alcohol synthesis (HAS) were prepared at different pH (6, 6.5, 7, 8, and 9) by co-precipitation to control Cu surface area and characterized by N₂ physisorption, XRD, SEM, H₂-TPR and TPD. The HAS reaction was carried out under a pressure of 45 bar, GHSV of 4000 h^?1, ratio of H₂/CO?=?1, and temperature ranges of 240 and 280 °C. It was found that the malachite phase of copper causes the size of copper to be small, which is suitable for methanol synthesis. Methanol and HAS share a common catalytic active site and intermediate. It was also found that the productivity to higher alcohol was correlated with Cu surface area.     

Synthesis and conversion of alcohols over modified transition metal sulphides

Alkali modified (Co/Ni)MoS systems are promising catalysts for higher alcohol synthesis from synthesis gas. The influence of various supports, modifiers and promoters on the activity of sulphide catalysts is reviewed. It is found that alkali metal reduces support acidity and affects the active phase morphology and active site functioning. Promotion of the catalyst with Co and Ni favours alcohol formation. KCoMoS catalyst activity in syngas conversion and hydrodesulphurization reactions is studied. An effect of organic compound additives such as methanol, ethanol, and ethylene on the catalyst behaviour is studied. It is suggested that alcohol formation may proceed in two steps: CO insertion and aldol condensation. Which of the two dominates depends on the reaction conditions.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Changes in the activity of Ru/Fe2O3 catalysts modified with alkali metal salts in the water-gas shift reaction

A study was undertaken to determine the activity of ruthenium catalysts, obtained by deposition of Ru₃(CO)₁₂ on products of iron oxide-hydroxide calcination modified with alkali metals, in the water-gas shift reaction. The activity depends on the kind of starting iron support, the ruthenium precursor and the amount of alkali metal salts. The most active were the catalysts obtained by deposition of Ru₃(CO)₁₂ on calcination products of σ-FeOOH, both modified and unmodified with alkali metal salts, and of α-FeOOH modified with alkali metal salts.     

Metal oxide-modified ZnO/SiO <Subscript>2</Subscript> catalysts for cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine

Metal oxide-modified ZnO /SiO2 catalysts were studied for the cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine at 633 K. The ZnO/SiO₂ catalyst showed fairly good ethylenediamine conversion and quantitative propyleneglycol conversion with about 60 mol% of 2-methylpyrazine selectivity, which is due to the existence of large amount of unconverted intermediate, 2-methylpiperazine. Metal oxide (CuO, NiO, Co₃O₄)-modified ZnO/SiO₂ catalysts were prepared to facilitate the dehydrogenation of 2-methylpiperazine to 2-methylpyrazine. About 82 mol% of 2-methylpyrazine selectivity was achieved on CuO and Co₃O₄ modified ZnO/SiO₂ catalysts, with significant increases of pyrazine selectivity. The catalytic properties of the metal oxidemodified ZnO/SiO₂ catalysts, pretreated with hydrogen gas as in the cyclo-dehydrogenation, were compared using the well-known probe reaction, the dehydrogenation/ dehydration of cyclohexanol to cyclohexanone or phenol/cyclohexene. The selectivities of pyrazine in the cyclo-dehydrogenation on the metal oxide-modified ZnO/SiO₂ catalysts were correlated with the phenol selectivities of the probe reaction. It is proposed that the metallic site of catalyst is responsible for the formation of pyrazine from ethylenediamine dimerization. The improved 2-methylpyrazine yield on CuO/ZnO/SiO₂ catalyst was explained by the proper adjustment of catalytic properties, which could be differentiated by the phenol selectivity in the cyclohexanol probe reaction. Thus, the large enhancement of 2-methylpiperazine dehydrogenation to 2-methylpyrazine and the suppression of excess pyrazine formation are supposed to occur on the metallic Cu formed in situ during the reaction during the cyclo-dehydrogenation of ethylenediamine with propyleneglycol.     

Thermogravimetric study of the carburization and coking of unsupported and carbon-supported Fe,Mo and Fe−Mo catalysts for fischer-tropsch synthesis

Carburization and coke deposition of unsupported and carbon-supported Fe, Mo and Fe?Mo catalysts in syngas have been studied using thermogravimetry. Compositions of the carbides formed are evaluated on the basis of the amount of metals in the catalysts and amount of carbon deposited during carburization. It is shown that carburization temperature and the nature of the carbides formed (Fe₅C₂ and Fe₂C for iron and Mo₂C for molybdenum) depend on the metals but are influenced by the support and metal loading. Coke deposition on these catalysts takes place as soon as carburization is complete.     

Non‐Oxidative Methane Conversion Using Lead‐ and Iron‐Modified Albite Catalysts in Fixed‐Bed Reactor

Raw and modified albite catalysts, including Pb/Albite and Fe/Albite catalysts, have been investigated for methane conversion to C₂ hydrocarbons under non‐oxidative conditions. Introduction of Pb to albite improved the activity and selectivity to non‐coke products. Based on characterization, it was found that Pb entered into the alkali and alkaline‐earth metal sites of albite, while partial Fe doped in the tetrahedron sites and the other loaded on the surface of albite. At the reaction temperature of 1073 K, methane gas hourly space velocity (GHSV) of 2 L·gcat^–1·h^–1, catalyst dosage of 0.25 g (300 mesh), the methane conversion catalyzed by raw albite in the fixed‐bed micro reactor exhibited a methane conversion of 3.32%. Notably, introducing a Pb content of 3.4 wt% into albite greatly enhanced the conversion of methane up to 8.19%, and the selectivity of C₂ hydrocarbons reached 99% without any coke under the same reaction conditions. While Fe‐doping could weakly heighten the methane conversion to 3.97%, and coke was formed. Thus, a comparison of Pb/Albite and Fe/Albite catalysts demonstrates that the catalytic activity of albite is mainly decided by alkali and alkaline‐earth metal sites, and lead‐modification can effectively improve the catalytic activity of albite.     

Hydrogenation of aromatic hydrocarbons in a mixture with thiophene on sulfided Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The activity and stability of aluminum-palladium catalysts in the hydrogenation of aromatic hydrocarbons mixed with thiophene were studied. The catalysts were obtained by impregnation of γ-A₂O₃ with aqueous solutions of salts of palladium complexes. Preliminary sulfiding followed by oxidative activation of Pd/Al₂O₃ catalysts were found to favor the formation of such palladium state on the surface at which the hydrogenation of aromatic hydrocarbons in the presence of sulfur-containing impurities proceeds without a noticeable change in the activity with time. IR spectroscopy showed that the palladium metal surface fragments forming CO complexes with a characteristic absorption band at 1998 cm^–1 are resistant to poisoning with sulfur-containing compounds in the hydrogenation of aromatic hydrocarbons.     

Recent Advances in Catalytic Decomposition of N<Subscript>2</Subscript>O on Noble Metal and Metal Oxide Catalysts

Catalytic decomposition of nitrous oxide (N₂O) is one of the most efficient methods for the removal of N₂O which is of high greenhouse potential and ozone-depleting property. Recent progress in the decomposition of N₂O has been reviewed with the focus on noble meal and metal oxide catalysts. The influence factors, such as catalyst support, preparation method, alkali metal additives and the reaction conditions (including O₂, H₂O, SO₂, NO and CO₂), on the performance of deN₂O catalysts have been discussed. Finally, future research direction for the catalytic decomposition of N₂O is proposed.     

Asymmetric Diels-Alder reaction of 1,3-butadienes with (−)-dimenthyl fumarate in the presence of BBr<Subscript>3</Subscript> and BBr<Subscript>3</Subscript>·OEt<Subscript>2</Subscript>

Asymmetric synthesis of substituted cyclohexenes was performed by [4+2]-cycloaddition of (-)-dimenthyl fumarate to 1,3-butadienes in the presence of BBr₃ and BBr₃·OEt₂. The latter are efficient catalysts for this reaction. The effect of various factors on the chemical and optical yield of compounds synthesized was studied. The lowering of the reaction temperature to ?70°C favors increase in the enantiomeric purity of products up to 81%. The overall yield of adducts grows with temperature and catalyst amount. The solvent character insignificantly affects the overall and optical yield of compounds obtained.     

Metal‐Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons

This study explores the kinetics, mechanism, and active sites of the CO₂ electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon‐based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO₂ to CO/H₂ mixtures outperforming a low‐area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low‐cost, abundant electrocatalysts for synthetic fuel production from CO₂.     

The Microstructure of Cobalt Silica Gel Catalyst in the Presence of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Additive

The physico-chemical characteristics and microstructure of cobalt silica gel catalysts with an Al₂O₃ additive (up to 10%) for the synthesis of hydrocarbons by the Fischer–Tropsch method are studied using a set of methods including X-ray diffraction, BET, IR spectroscopy, and temperature-programmed reduction of H₂, as well as scanning and transmission electron microscopy. Phases with a spinel structure, Со₃О₄, CoAl₂O₄, and solid solutions on their basis are identified in the samples. The addition of Al₂O₃ changes the degree of heterogeneity and the orientation of the cobalt crystallites in the oxide and reduced forms of the catalysts. Addition of 1% Al₂O₃ stabilizes Со₃О₄ in the spinel form with a structure close to the normal one and promotes the formation of cobalt with a unimodal distribution of particles with an average size of 8 nm. The catalyst is characterized by maximum activity and selectivity with respect to C⁵⁺ carbons.     

The catalytic performance of different promoted iron catalysts on combined supports Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for carbon dioxide hydrogenation

Global warming, fossil fuel depletion and fuel price increases have motivated scientists to search for methods for the storage and reduction of the amount of greenhouse gases, especially CO₂. The hydrogenation process has been introduced as an emerging method of CO₂ capture and convertion into value-added products. In this study, new types of catalysts are introduced for CO₂ hydrogenation and are compared based on catalytic activity and product selectivity. The physical properties of the samples are specified using BET. Iron catalysts supported on γ-Al₂O₃ with different metal promoters (X = Ni, K, Mn, Cu) are prepared through the impregnation method. Moreover, Fe–Ni catalysts supported on HZSM5-Al₂O₃ and Ce–Al₂O₃ are synthesized. Samples are reduced by pure H₂ and involved in hydrogenation reaction in a fixed bed reactor (H₂/CO₂ = 3, total pressure = 10 MPa, temperature = 523 K, GHSV = 2000, 1250 nml/min). All catalysts provide high conversion in hydrogenation reactions and the results illustrate that the selectivity of light hydrocarbons is higher than that of methane and CO. It is found that Ni has a promoting effect on the conversion fluctuations throughout the reaction with 66.13% conversion. Using combined supported catalysts leads to enhancing catalytic performance. When Fe–Ni/γ–Al₂O₃—HZSM5 is utilized, CO₂ conversion is 81.66% and the stability of the Fe–Ni catalyst supported on Al₂O₃ and Ce–Al₂O₃ furthey improves.     

Effect of chemical modification on oligomerization capacity of alumina support for Pd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Effect of modification with an alkali metal on the acid properties of alumina supports and on the oligomerization capacity and working stability of Pd-Al₂O₃ catalysts was studied.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

Influence of the composition of perovskites based on SrMnO<Subscript>3</Subscript> on their catalytic properties in the oxidative coupling of methane

The oxidative coupling of methane (OCM) in a periodic regime over the SrMnO₃ and its derivatives has been investigated. It has been established that partial replacement of the strontium ion by alkali metal ions leads to an increase in both catalytic activity and in selectivity with respect to higher hydrocarbons. Comparison of the results obtained in the present work with those obtained earlier for catalysts based on SrCoO₃ led to the conclusion that the Co-containing catalysts were preferable to the Mn-containing catalysts for carrying out oxidative coupling of methane in a periodic regime.__________Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 41, No. 1, pp. 30–34, January–February, 2005.     

贵金属助剂对费-托合成用钴基催化剂的促进作用

贵金属助剂促进的费-托合成用钴基催化剂具有高活性和长链烃(C₅⁺)选择性优越等特点,被广泛应用于由合成气制清洁燃料的合成反应中。 本文重点讨论了贵金属助剂对活性钴物种的结构（还原度、分散度、双金属颗粒或合金的构成）, 钴基催化剂稳定性以及其对费-托合成的反应速率和产物选择性的影响规律。     

Cycloolefin polymerization initiated by transition metal–π-allylic complexes

A new class of catalysts for polymerization of cycloalkenes was developed, based on the interaction of these hydrocarbons with π-allylic transition metal complexes. The reaction route (decyclization or double-bond opening) and the microstructure of polyalkenamers obtained is determined primarily by the nature of the transition metal and also by the nature and the number of ligands bound to the metal. π-Allylic complexes of zirconium and chromium catalyze the polymerization of cycloalkenes in both directions. For complexes of the group VI metals the substitution of molybdenum or tungsten for chromium results in complete suppression of the double-bond opening. In the presence of Group VIII metal compounds the polymerization of cycloolefins occurs exclusively at the double bond. The introduction of acidic ligands into the internal sphere of the π-allylic compound does not affect the reaction route but results in a significant rise of the yield of polyalkenamers and enriches the content of trans-1,4-units. Lewis acids act as activators for complexes of all the metals, the halides of molybdenum and tungsten affecting favorably the decyclization. It is assumed that the ring-opening polymerization of cycloolefins proceeds via π-allylic complex formation.     

Cobalt boride catalysts for hydrogen storage systems based on NH<Subscript>3</Subscript>BH<Subscript>3</Subscript> and NaBH<Subscript>4</Subscript>

The catalytic activity of cobalt borides forming in situ under conditions of NH₃BH₃ and NaBH₄ hydrolysis have been investigated. The reaction properties of the catalysts depend on the nature of the hydride. According to high-temperature X-ray diffraction, thermal analysis, high-resolution transmission electron microscopy, IR spectroscopy, and chemical analysis data, the nature of the hydride determines the particle size, chemical composition, and crystallization properties of the cobalt borides.     

A comparative study of Ir/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, Pt/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Ru/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in selective hydrogenation of crotonaldehyde

Catalytic performance of gallia-supported iridium catalysts in the reaction of selective hydrogenation of crotonaldehyde in the gas phase was studied and compared to that of platinum and ruthenium catalysts. The best catalytic properties in terms of the selectivity to crotyl alcohol are shown by 5 wt % Pt/α-Ga₂O₃ and 5 wt % Ir/α-Ga₂O₃ catalysts prepared from nonchlorine precursors: Pt(acac)₂ and Ir(acac)₃, but for the 5 wt % Pt/α-Ga₂O₃ a very high selectivity of 75% at the high conversion (ca. 60%) is observed. A high selectivity of galia-supported iridium and platinum catalysts was explained by the surface reducibility of gallium oxide leading to covering (decoration) of platinum and iridium by gallium suboxides and the promoting effect of gallium.