Catalytic behavior of chromium oxide supported on nanocasting-prepared mesoporous alumina in dehydrogenation of propane

Mesoporous alumina with narrow pore size distribution centered in the range of 4.4–5.0 nm and with a specific surface area as high as 270 m2·g−1 was prepared via the nanocasting approach using a CMK-3 carbon replica as a hard template. Based on this support, a series of catalysts containing 1, 5, 10, 20 and 30 wt % of chromium was prepared by incipient wetness impregnation, characterized, and studied in the dehydrogenation of propane to propene (PDH). Cr species in three oxidation states—Cr(III), Cr(V) and Cr(VI)—were found on the oxidized surface of the catalysts. The concentration of these species varied with the total Cr loading. Temperature-programmed reduction (H2-TPR) and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS) studies revealed that Cr(VI) species dominated at the lowest Cr content. An increase in the Cr loading resulted in an appearance of an increasing amount of Cr(III) oxide. UV-Vis-DRS measurements performed in situ during the PDH process showed that at the beginning of the catalytic test Cr(VI) species were reduced to Cr(III) redox species. A crucial role of the redox species in the PDH process over the catalysts with the low Cr content was confirmed. The stability test for the catalyst containing 20 wt % of Cr showed that this sample exhibited the reproducible catalytic performance after the first four regeneration–dehydrogenation cycles. Moreover, this catalyst had higher resistance on deactivation during the PDH process as compared to the reference catalyst with the same Cr loading, but was supported on commercially available alumina

Preparation and characterization of SBA-1-supported chromium oxide catalysts for CO2CO_{2} assisted dehydrogenation of propane

A series of Crx/SBA-1 cubic mesoporous catalysts with 1, 3, 5, 7, 10, and 15 wt.% content of Cr (Crtotal) were obtained by incipient wetness impregnation of SBA-1. The obtained catalysts were characterized with various physicochemical techniques (chemical composition, low-temperature adsorption of N2, H2–TPR, XRD, UV–vis DRS, Raman, and EPR) and tested in dehydrogenation of propane to propene in the presence of CO2. Various chromium species including Cr6+, dispersed Cr5+, and crystalline Cr2O3 were found in the calcined Crx/SBA-1 samples. Cr6+ species were present mainly in the form of mono- and dichromates, despite the Cr loading. The presence of dispersed Cr5+ species and crystalline α-Cr2O3 in the calcined catalysts depended on the total Crtotal content. Cr5+ species were found in the samples containing below 7 wt.% of Crtotal, while particles of crystalline α-Cr2O3 were detected in the catalyst with Crtotal content above 5 wt.%. All of the Crx/SBA-1 catalysts exhibited excellent catalytic activity and high selectivity in the dehydrogenation of propane to propene in the presence of CO2 with the maximum propane conversion (37.7% at 550 °C) for ∼7 wt.% of Crtotal. For higher Cr contents the conversion of propane remained almost constant which was connected with the formation of crystalline Cr2O3 which was inactive in the test reaction. Operando UV–vis DRS measurements performed during the dehydrogenation of propane, both in the presence and absence of CO2 at 550 °C, indicated that the Cr6+ species (main redox sites) were reduced rapidly to Cr2+/Cr3+ species already at the beginning of the process. The dispersed Cr2+/Cr3+ ions were the main sites available to the reactants under the dehydrogenation conditions in all of the studied feed compositions

3D Printing in Heterogeneous Catalysis—The State of the Art

This paper describes the process of additive manufacturing and a selection of three-dimensional (3D) printing methods which have applications in chemical synthesis, specifically for the production of monolithic catalysts. A review was conducted on reference literature for 3D printing applications in the field of catalysis. It was proven that 3D printing is a promising production method for catalysts

Catalytic performance of sucrose-derived CMK-3 in oxidative dehydrogenation of propane to propene

CMK-3 carbon replica was synthesized by carbonization of sucrose introduced to the pore system of a SBA- 15 hard template followed by dissolving SiO 2 with HF. The material with a stable hexagonal structure and an expanded surface area ( S BET = 1287 m 2 /g) was obtained. TG measurements showed that CMK-3 type mesoporous carbon started to be intensively oxidized by molecular O 2 above 723 K. This carbon sample was tested as a catalyst of dehydrogenation of propane to propene under oxidative (O 2 :C 3 H 8 = 0.25, 0.50 and 1.00) and non-oxidative (O 2 :C 3 H 8 = 0.00) conditions in the temperature range from 573 to 873 K. The propene yield increased with rise in the reaction temperature, however above 573 K the formation of side- products (C 2 H 6 , C 2 H 4 , CH 4 and H 2 ) was observed. Moreover, coke was deposited on the catalyst surface. A decrease in the mass of a catalyst bed after the catalytic runs suggested the participation of oxygen in burning of deposited and bulk coke. The surface composition of a spent catalyst was investigated by XPS and TPD analysis. The changes in the concentration of oxygen functional groups, caused by the catalytic reaction, were observed regardless of a reaction temperature and feed composition