A comparison of the reactivities of propanal and propylene on HZSM-5

a b s t r a c t The reactivities of propanal and propylene have been compared over HSZM-5 zeolites (Si/Al = 45 and 25). Propanal is found to be much more reactive than propylene and to form mostly 2-methyl-2-pentenal and C 9 aromatics as early products in the reaction network. Propylene, in contrast, requires more severe conditions to form C 6 and C 7 aromatics. It is proposed that propanal undergoes acid-catalyzed aldol condensation to form 2-methyl-2-pentenal. This dimer undergoes further condensation to form the aldol trimer, which subsequently dehydrates and cyclizes into C 9 aromatics. In contrast, it is well known that propylene, like other olefins, undergoes aromatization via oligomerization and formation of a hydrocarbon pool. While in the conversion of propanal, propylene is also produced, it appears that it does not play a major role in the formation of aromatics under conditions of shorter space times and lower temperatures, at which propanal produces aromatics in significant amounts

Deoxygenation of benzaldehyde over CsNaX zeolites

The deoxygenation of benzaldehyde to benzene and toluene was investigated on basic CsNaX, and NaX zeolite catalysts. It was observed that as-prepared CsNaX, containing Cs in excess, displays high activity for direct decarbonylation of benzaldehyde to benzene. However, in parallel with the decarbonylation reaction, condensation of surface products occurs. Therefore, the lower pore volume of catalyst having excess Cs leads to lower catalyst stability. Decomposition of surface condensation products results in further evolution of benzene and toluene. It is observed that gas-phase H2 can play an important role by reducing the residence time of surface intermediates, thus decreasing the amount of condensation products that accumulate and lead to catalyst deactivation. Hydrogen transfer to the condensation surface products accelerates the decomposition of these condensation compounds primarily into toluene. NaX catalyst and washed CsNaX do not exhibit a high initial activity for direct decarbonylation, but rather operate via formation of surface condensation products which subsequently decompose yielding benzene and toluene. The residual acidity present in NaX catalysts causes a faster deactivation for this catalyst than for those containing Cs.Fil: Peralta, María Ariela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Sooknoi, Tawan. Oklahoma State University; Estados UnidosFil: Danuthai, Tanate. Oklahoma State University; Estados UnidosFil: Resasco, Daniel E.. Oklahoma State University; Estados Unido

High Surface Area ZnO-Nanorods Catalyze the Clean Thermal Methane Oxidation to CO₂

ZnO nanostructures were synthesized by a combination of non-aqueous and aqueous sol-gel techniques to obtain morphologically different ZnO nanostructures, nanorods, and nanopyramids, featuring oxygen vacancies-rich exposed lattice faces and exhibiting different catalytic properties and activity. In particular, ZnO nanorods with high surface area (36 m2/g) were obtained through a rapid, scalable, and convenient procedure. The materials were tested for complete methane oxidation as an important benchmark reaction that is sensitive to surface area and to the availability of oxygen vacancies. Simple ZnO nanorods derived from nanosized quantum dots showed the best catalytic performance that compared well to that of several literature-reported perovskites, mixed metal oxides, and single-metal oxides in terms of T50 (576 °C) and T90 (659 °C) temperatures. Such a result was attributed to their high surface-to-volume ratio enhancing the availability of catalytically active sites such as oxygen vacancies whose abundance further increased following catalytic application at high temperatures. The latter effect allowed us to maintain a nearly stable catalytic performance with over 90% conversion for 12 h at 700 °C despite sintering. This research shows that ZnO-based nanomaterials with a high surface area are viable alternatives to oxides of commonly applied (but of potentially limited availability) transition metals (La, Mn, Co, Ni) for the complete combustion of methane when working at moderate temperatures (600–700 °C)

High Surface Area ZnO-Nanorods Catalyze the Clean Thermal Methane Oxidation to CO2

ZnO nanostructures were synthesized by a combination of non-aqueous and aqueous sol-gel techniques to obtain morphologically different ZnO nanostructures, nanorods, and nanopyramids, featuring oxygen vacancies-rich exposed lattice faces and exhibiting different catalytic properties and activity. In particular, ZnO nanorods with high surface area (36 m2/g) were obtained through a rapid, scalable, and convenient procedure. The materials were tested for complete methane oxidation as an important benchmark reaction that is sensitive to surface area and to the availability of oxygen vacancies. Simple ZnO nanorods derived from nanosized quantum dots showed the best catalytic performance that compared well to that of several literature-reported perovskites, mixed metal oxides, and single-metal oxides in terms of T50 (576 °C) and T90 (659 °C) temperatures. Such a result was attributed to their high surface-to-volume ratio enhancing the availability of catalytically active sites such as oxygen vacancies whose abundance further increased following catalytic application at high temperatures. The latter effect allowed us to maintain a nearly stable catalytic performance with over 90% conversion for 12 h at 700 °C despite sintering. This research shows that ZnO-based nanomaterials with a high surface area are viable alternatives to oxides of commonly applied (but of potentially limited availability) transition metals (La, Mn, Co, Ni) for the complete combustion of methane when working at moderate temperatures (600–700 °C)

Condensation reactions of propanal over Ce x Zr 1−x O 2 mixed oxide catalysts

a b s t r a c t Vapor phase condensation reactions of propanal were investigated over Ce x Zr 1−x O 2 mixed oxides as a model reaction to produce gasoline range molecules from short aldehydes found in bio-oil mixtures. Several operating parameters were investigated. These included the type of carrier gas used (H 2 or He) and the incorporation of acids and water in the feed. Propanal is converted to higher carbon chain oxygenates on Ce x Zr 1−x O 2 by two pathways, aldol condensation and ketonization. The major products of these condensation reactions include 3-pentanone, 2-methyl-2-pentenal, 2-methylpentanal, 3-heptanone and 4-methyl-3-heptanone. It is proposed that the primary intermediate for the ketonization path is a surface carboxylate. The presence of acids in the feed inhibits the aldol condensation pathway by competitive adsorption that reduces the aldehyde conversion. Water also promotes ketonization and inhibits aldol condensation by increasing the concentration of surface hydroxyl groups that enhance the formation of surface carboxylates with the aldehyde. Hydrogen enhances cracking and production of light oxygenates and hydrocarbons. The light oxygenates may in turn be reincorporated into the reaction path, giving secondary products. However, the hydrocarbons do not react further. Analysis of the fresh and spent catalysts by XPS showed varying degrees of reduction of the oxide under different operating conditions that were consistent with the reaction results. Changing the proportion of the parent oxides showed that increased Zr favored formation of aldol products while increased Ce favored ketonization. This occurs by shifting the balance of the acid-base properties of the active sites

Development of bimetallic Ni-Cu/SiO2 catalysts for liquid phase selective hydrogenation of furfural to furfuryl alcohol

International audienceBimetallic Ni-Cu/SiO 2 catalysts with different Cu loading (2-5 wt%) were developed for liquid phase selective hydrogenation of furfural to furfuryl alcohol. Among these, bimetallic 2%Ni-X%Cu/SiO 2 (X = 2, 5) catalysts exhibited better catalytic performances than monometallic 2%Ni/SiO 2 and 2%Cu/SiO 2. Moreover, the bimetallic 2%Ni-5%Cu/SiO 2 catalyst showed the best catalytic performance with 94% of furfural conversion and 64% of furfuryl alcohol selectivity. The synergetic effect of NiCu alloy particles that are present on bimetallic Ni-Cu/SiO 2 catalysts change the adsorption configuration of furfural on the catalyst surface resulting in high catalytic performance in liquid phase selective hydrogenation of furfural to furfuryl alcohol

Development of bimetallic Ni-Cu/SiO2 catalysts for liquid phase selective hydrogenation of furfural to furfuryl alcohol

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