S.B. Kogan

Dehydrogenation of propane on modified Pt/θ-alumina Performance in hydrogen and steam environment

Dehydrogenation of propane was carried out on several promoted Pt catalysts. The performance of the catalysts (activity, selectivity and coke formation) was compared in steam and hydrogen environment. Promoting Pt supported on θ-alumina with Sn and K is essential for developing high-performance catalysts. The combination of optimal catalyst composition and steam yields high activity and selectivity at low coke formation. Inferior results were measured with hydrogen as diluent. Characterization of catalysts using XPS, TEM and chemisorption methods supported the results of reaction data.

Selectivity in heterogeneous catalytic processes

Abstract The selectivity of several catalytic systems was studied. Shape selectivity of Pt on carbon-fiber catalysts was demonstrated in the competitive hydrogenation of 1-hexene and cyclohexene and in the parallel dehydrogenation of cyclohexanol to cyclohexanone and phenol. Both reactions were carried out in a gas-phase fixed-bed reactor. Catalysts prepared on carbon fibers, containing pores with small constrictions (5 A) yielded significantly higher rates of hydrogenation of 1-hexene compared to those of cyclohexene and selectively produced cyclohexanone from cyclohexanol. Other catalysts, supported on carbon fibers with large constrictions (7 A) or activated carbon, displayed comparable rates of hydrogenation for both reactants and yielded cyclohexanone as well as phenol from cyclohexanol. Nitration of o -xylene with nitrogen dioxide was carried out in the gas phase over a series of solid acid catalysts packed in a fixed bed. Several zeolites, supported sulfuric acid, and sulfated zirconia were tested. Zeolite H-β was found to be the most active and selective catalyst for the production of 4-nitro- o -xylene. A preliminary kinetic model indicated that the selectivity to 4-nitro- o -xylene increased with decreasing concentration of nitrogen dioxide. Alkylation of phenol with methanol was performed on zeolites, supported sulfuric and phosphoric acids, and sulfated zirconia packed in a fixed-bed. The ratio of o - to c -alkylation, measured at 180°C and methanol to phenol feed molar ratio of unity, ranged from 4 with the supported acids to 2 with zeolite H-β. This ratio decreased with temperature. The ratio of o - to p -cresol changed from about 2 in zeolites in supported sulfuric acid and to 0.5 in phosphoric acid supported on carbon fibers.

Novel nitrogen containing heterogeneous catalysts for oxidative dehydrogenation of light paraffins

Abstract Novel nitrogen contained catalyst CoNx/Al2O3 yielded high performance in the oxidative dehydrogenation of propane and n-butane. 47.6 and 37.4 wt% yield of olefins at 82% butane and 76.7% propane conversion were measured at 600 °C. Ethylene and propylene were mainly formed at >400 °C via oxidative cracking of paraffins. XRD and XPS studies of the novel catalytic system indicate an essential modification of cobalt by nitrogen.

Deactivation of a multimetal supported catalyst for anilineN-alkylation with alcohol

Abstract A multicomponent catalyst, containing platinum, tin and calcium on a silica gel support was tested for N -alkylation of MeEt-aniline (MEA) with methoxyisopropanol in a continuous fixed bed reactor at atmospheric pressure in the presence of hydrogen. It was found that the active Pt-Sn-Ca phase is located in the macro pores of the silica carrier; it has an average crystallite diameter of 55–165Aand a crystallinity degree of 30–90%, depending upon the activation-working conditions, and after reduction it contains Pt 3 Sn alloy. Catalyst deactivation is caused by the formation of a strongly bonded coke layer containing nitrogen, which interacts with the Pt-component leading to the formation of a surface complex Pt...N with electron transfer from nitrogen to Pt. ‘ Pure ’ coke (without nitrogen) up to 4 wt.-% does not affect the catalyst activity/selectivity. The amount of N-containing coke depends upon MEA purity and operational conditions controlling the reaction selectivity. The strongly poisoning N-containing coke is produced by the red-colored oxidation-condensation products present in crude MEA and/or by a relatively high concentration of intermediate N -isopropylidenemethoxy-MeEt-aniline (IM) in the reactor. The IM concentration depends upon operational conditions and catalyst composition. Cleaning of crude MEA by distillation and adsorption of heavy impurities on silica and operating at proper conditions yielded low IM concentration with a stable yield of N -isopropylmethoxy -MeEt-aniline 63–65% and selectivity about 95% within a 200 h period of operation. The N-containing coke cannot be removed by treatment of the catalyst with nitrogen or hydrogen, but oxidative regeneration allows to reestablish the active phase with the same initial activity / selectivity patterns.

Shape—Selectivity of Pt On Carbon Fibers Catalysts

Abstract Catalysts were prepared by impregnation of Pt inside the pore structure of carbon fibers. Care was taken to eliminate the active metal from the external surface of the support. A very high dispersion of Pt was measured. Four reactions were carried out in a fixed-bed reactor: competitive hydrogenation of cyclohexene and 1-hexene, cyclization of 1-hexene, n-heptane conversion and dehydrogenation of cyclohexanol. Three types of carbon fibers with a different pore size and Pt-adsorption capacity along with a Pt on activated carbon commercial catalyst were tested. The data indicate a significant effect of the pore size dimension on the selectivity in each system. The ability to tailor the pore structure to achieve results drastically different from those obtained with established supports is demonstrated with heptane conversion. Pt on open pore carbon fibers show higher activity with the same selectivity as compared with Pt on activated carbon catalysts.

Dehydrogenation of methoxyisopropanol to methoxyacetone on supported bimetallic Cu-Zn catalysts

Dehydrogenation of methoxyisopropanol (MOIP) on reduced Cu-Zn catalysts was studied in a fixed bed reactor at 200–300°C and atmospheric pressure. Alumina supported catalysts yielded a lower initial activity compared with the silica supported catalysts and displayed a lower deactivation rate. The main route for deactivation of Cu-Zn/Al 2 O 3 was coking while that of Cu-Zn/SiO 2 was the crystallization of Cu o phase. ZnO was essentially an inactive component, promoted the activity of supported Cu catalysts by modifying the structure and electronic state of Cu metallic phase and selectivity of Cu/Al 2 O 3 by modifying the surface of support. Oxidative regeneration of Cu-Zn/Al 2 O 3 catalyst after 250 hours on stream recovered completely its initial activity. Kinetic experiments yielded a Langmuir-Hinshelwood type equation expressing the MOIP rate of dehydrogenation on Cu-Zn/Al 2 O 3