Production, Physicochemical and Catalytic Properties of Gallium-Containing Zeolite Catalysts

Crystalline galloalumino- and gallosilicates with pentasil structure were synthesised under hydrother-mal conditions. The influence of gallium concentration and binder amount both on physicochemical and catalytic properties of a zeolite in the process of C2-C4 light alkanes aromatization and on catalyst deacti-vation due to carbidization has been studied. Acidic properties of gallium-containing pentasils with differ-ent composition were studied using the method of thermoprogrammed ammonia desorption. The forma-tion of strong aproton acidic sites whose composition includes gallium ions was found. It has been shown that isomorphic aluminium replacement by gallium in the pentasil lattice leads to a significant increase in aromatizing activity and period of stable catalyst operation. A decrease in intensity of coking and the formation of less condensed coke deposits with a wide distribution by the structure are observed with the increase in gallium concentration. The introduction of a binder to galloaluminosilicate results in a signifi-cant increase in mechanical strength of a catalyst. It was established that the most efficient catalyst of the above process is a zeolite containing 2.2% of gallium oxide and 1.3% of aluminium oxide and mixed with 20% of the pseudobeumite. The selectivity of the formation of aromatic hydrocarbons reaches 55-60%, the period of stable operation exceeds 350 h. In accordance with the data obtained suggested are the principles of the selection of efficient catalysts of light alkanes aromatization and optimum conditions of the process

Generation of Liquid Products from Natural Gas over Zeolite Catalysts

The main component of the natural gas is methane, whose molecules are characterized by a high chemical and thermal stability. It is impossible to perform the chemical transformation of natural gas into liquid organic compounds without applying highly active polyfunctional catalysts. Natural gas might be converted into liquid products in the presence of zeolite catalysts of pentasil family. Zeolite catalysts of ZSM-5 type were prepared to realize the process. They contained various amounts of Zn and Ga promoters introduced by ion exchange and impregnation. It has been shown that in the presence of small amounts of C2-C5 alkanes in the feedstock the methane is converted into aromatic hydrocarbons much more readily and in softer conditions than pure methane. At optimum process conditions reached is a high conversion of the natural gas into a mixture of aromatic hydrocarbons. This mixture mainly consists of benzene and naphthalene and small amounts of their derivatives – toluene, C8 and C9+ alkylbenzenes, methyl- and dimethylnaphthalenes. An optimum composition of zeolite matrix and the amount of the modifier in the catalyst have been established

A Model of Catalytic Cracking: Product Distribution and Catalyst Deactivation Depending on Saturates, Aromatics and Resins Content in Feed

The problems of catalyst deactivation and optimization of the mixed feedstock become more relevant when the residues are involved as a catalytic cracking feedstock. Through numerical and experimental studies of catalytic cracking, we optimized the composition of the mixed feedstock in order to minimize the catalyst deactivation by coke. A pure vacuum gasoil increases the yields of the wet gas and the gasoline (56.1 and 24.9 wt%). An increase in the ratio of residues up to 50% reduces the gasoline yield due to the catalyst deactivation by 19.9%. However, this provides a rise in the RON of gasoline and the light gasoil yield by 1.9 units and 1.7 wt% Moreover, the ratio of residue may be less than 50%, since the conversion is limited by the regenerator coke burning ability

Production of Aromatic Hydrocarbons from C3, C4-alkanes over Zeolite Catalysts

Гидротермальным способом из щелочных алюмокремнегелей синтезированы алюмосиликат и галлоалюмосиликат структурного типа MFI. Исследованы структурные, кислотные и каталитические свойства полученных цеолитов в процессе дегидроциклизации низших алканов. Установлено, что наибольшее количество ароматических углеводородов образуется при превращении бутана на галлоалюмосиликате, а наименьшее – при превращении пропана на алюмосиликате. Показано, что для достижения близкой конверсии пропана и бутана и выхода целевого продукта в присутствии изученных катализаторов температура процесса при превращении пропана должна быть на 50 градусов выше при одинаковых других условиях реакцииAn aluminosilicate and a galloaluminosilicate of MFI structure are synthesized by the hydrothermal method from alkaline aluminosilicates. Structural, acidic, and catalytic properties of synthesized zeolites are investigated in the course of dehydrocyclization of lower alkanes. It is found out that aromatic hydrocarbons are formed in their highest amount when butane is converted over the galloaluminosilicate, while the lowest amount of them is resulted from the conversion of propane over the aluminosilicate. It is shown that to achieve the nigh conversion of propane and butane and the yield of desired product in the presence of the catalysts under study, the process temperature during the propane conversion should be 50 degrees higher under the same other reaction condition

Low-temperature CO oxidation on Ag/ZSM-5 catalysts: Influence of Si/Al ratio and redox pretreatments on formation of silver active sites

Silver catalysts supported on ZSM-5 (Si/Al = 30, 50 and 80) were investigated for low-temperature CO oxidation to study the nature of the silver active sites and their formation under the influence of the support chemical composition and redox pretreatments. The catalysts were characterized by HRTEM, FTIR, XPS, diffuse reflectance UV–Vis spectroscopy, NH3 thermodesorption (NH3 TPD) and temperature-programmed reduction (H2 TPR). The chemical composition (Si/Al ratio) of the ZSM-5 zeolite support significantly affects catalytic properties of Ag/ZSM-5 samples: the lower the Broensted acidity of the zeolite support, the higher the activity of the catalysts. Interestingly, while oxidizing pretreatment of catalysts led to a significantly better performance than reducing pretreatments, the consecutive reducing treatment of the preoxidized samples significantly promoted the catalytic activity for low-temperature CO oxidation. Thus, Ag/ZMS-5 catalyst with Si/Al = 80, pretreated consecutively in oxidizing and reducing conditions, showed the highest activity, reaching 90% CO conversion at just 40 °C. Comparison of activity and characterization results showed that silver particles with size below 2 nm are the most active; larger particles are just “spectators”. The most probable silver active centers in the low-temperature CO oxidation are ionic species, mostly charged clusters Agnδ+, strongly interacting with the support. The obtained results in low-temperature CO oxidation might be of particular interest for neutralization of exhaust gases of car engines during “cold start”

Low-temperature CO oxidation on Ag/ZSM-5 catalysts: Influence of Si/Al ratio and redox pretreatments on formation of silver active sites

Silver catalysts supported on ZSM-5 (Si/Al = 30, 50 and 80) were investigated for low-temperature CO oxidation to study the nature of the silver active sites and their formation under the influence of the support chemical composition and redox pretreatments. The catalysts were characterized by HRTEM, FTIR, XPS, diffuse reflectance UV–Vis spectroscopy, NH3 thermodesorption (NH3 TPD) and temperature-programmed reduction (H2 TPR). The chemical composition (Si/Al ratio) of the ZSM-5 zeolite support significantly affects catalytic properties of Ag/ZSM-5 samples: the lower the Broensted acidity of the zeolite support, the higher the activity of the catalysts. Interestingly, while oxidizing pretreatment of catalysts led to a significantly better performance than reducing pretreatments, the consecutive reducing treatment of the preoxidized samples significantly promoted the catalytic activity for low-temperature CO oxidation. Thus, Ag/ZMS-5 catalyst with Si/Al = 80, pretreated consecutively in oxidizing and reducing conditions, showed the highest activity, reaching 90% CO conversion at just 40 °C. Comparison of activity and characterization results showed that silver particles with size below 2 nm are the most active; larger particles are just “spectators”. The most probable silver active centers in the low-temperature CO oxidation are ionic species, mostly charged clusters Agnδ+, strongly interacting with the support. The obtained results in low-temperature CO oxidation might be of particular interest for neutralization of exhaust gases of car engines during “cold start”

Кинетические особенности процесса превращения пропана в ароматические углеводороды

Kinetic features of the propane conversion into aromatic hydrocarbons over a gallium-containing zeolite catalyst have been investigated. On the basis of the experimentally obtained kinetic dependences and the available literature data, a kinetic model of propane aromatization is proposed, which makes it possible to form various variations of chemical reaction behavior and to calculate the most probable routes of propane conversionПроведено исследование кинетических особенностей процесса превращения пропана в ароматические углеводороды на галлийсодержащем цеолитном катализаторе. На основе экспериментально полученных кинетических зависимостей и имеющихся литературных данных предложена кинетическая модель ароматизации пропана, позволяющая сформировать различные варианты протекания химических реакций, рассчитать наиболее вероятные маршруты превращения пропан