The study of CrOx-containing catalysts supported on ZrO2, CeO2, and CexZr(1-x)O2 in isobutane dehydrogenation

Olefin hydrocarbons are valuable raw materials for petrochemical and polymer manufacturing. Highly effective, but toxic chromium-containing catalytic materials are the most widely used catalysts to obtain olefins in industry. In this regard, the urgent challenge to increase the efficiency of oil processing is to develop the catalysts with low content of harmful active component. In the present study, the catalysts with low chromium content (1 theoretical monolayer = 5 Cr atoms per nm2 of support) were synthesized by incipient wetness impregnation of the supports (Al2O3, ZrO2, CeO2, and Ce x Zr(1–x)O2). The samples obtained were characterized by low-temperature nitrogen adsorption, X-ray diffraction and H2-temperature-programmed reduction methods. The catalytic properties of the catalysts were tested in isobutane dehydrogenation reaction. It was shown that the state of chromium on the surface is different over different supports. For the CrO x /CeO2 catalyst, the formation of Cr2O3 particles with low activity in the dehydrogenation reaction was observed. For other samples, a highly disperse X-ray amorphous state of chromium was characteristic. The catalyst based on Ce x Zr(1–x)O2 was the most active in isobutane dehydrogenation reaction due to possible stabilization of chromium as Cr(V) state

Разработка SiO2 материалов с иерархической структурой и Pt-Ga катализаторов на их основе для дегидрирования пропана

В данной работе проведен синтез силикатного носителя с иерархической пористой структурой на основе диатомита и MCM-41. Особенностью синтеза является то, что МСМ-41 образуется непосредственно на поверхности диатомита и из самого диатомита, без использования дополнительных предшественников оксида кремния Исследование пористой структуры полученного носителя проводили методом низкотемпературной адсорбции азота (-196 C), для изучения структуры поверхности материала был использован метод сканирующей электронной микроскопии (СЭМ). Показано, что разработанный подход позволяет получать носители на основе диатомита и MCM-41, характеризующиеся иерархической структурой и высокими значениями удельной поверхности

Al2O3/SiO2 materials with bimodal pore size distribution as support for heterogeneous catalysts

The Al2O3/SiO2 materials prepared by impregnation of mesoporous silica with water solution of Al(NO3)3·9H2O were suggested to be used as supports for catalyst of high-temperature catalytic reactions. It was shown that the distribution of Al2O3 component inside wide pores of silica (10-50 nm) occurs with the formation of Al2O3 layer in case of low loading and porous layer or particles, if Al2O3 loading increases. Thus, materials with bimodal pore size distribution were obtained. The Cr-containing catalysts were prepared on the basis of these supports and tested in the process of isobutane dehydrogenation at 540 °C. It was observed that the activity of the obtained Cr/Al2O3/SiO2 materials was comparable with the one for Cr/Al2O3 catalyst. Thus, the suggested Al2O3/SiO2 materials with unique porous structure are promising to be used as supports for catalysts for high-temperature reactions.</jats:p

Effect of zirconia additives on the activity of the Cr/SiO2 catalyst in isobutane dehydrogenation

A new approach to the preparation of modified silica-based supports is suggested to obtain Crcontaining catalysts for paraffin hydrocarbon dehydrogenation. CrOx/ZrO2, CrOx/SiO2, and CrOx/nZrO2–SiO2 (n = 0.5, 1.0, and 2.0 ZrO2 monolayers) catalysts have been synthesized by incipient-wetness impregnation. The catalysts have been characterized by X-ray diffraction, diffuse reflectance spectroscopy, and temperature-programmed reduction with hydrogen. Their catalytic properties were investigated in the reaction of isobutane dehydrogenation. The state of the supported chromium depends considerably on the nature of the support. The formation of Cr2O3 particles, which show low activity in the dehydrogenation reaction, takes place in the CrOx/SiO2 catalyst, while chromium in the CrOx/ZrO2 catalyst is in a highly dispersed, X-ray-amorphous state. The addition of ZrO2 to CrOx/SiO2 increases the amount of chromium in the highly dispersed Cr(V) and Cr(VI) states, thus enhancing the isobutane dehydrogenation activity of the catalyst

Cr2O3/Al-Al2O3 composite catalysts for hydrocarbons dehydrogenation prepared from aluminum nanopowder

Aluminum nanopowder (10–150 nm) was treated hydrothermally in mild conditions (60–95 °C, at atmospheric pressure), and an aluminum-alumina composite with high porosity and specific surface area was obtained. Cr2O3/Al-Al2O3 catalysts were prepared using the aluminum-alumina composite by impregnation techniques and tested in dehydrogenation of C4-hydrocarbons. It was shown that aluminum-alumina composites had high chemical and phase purity, specific surface area of 150–350 m2/g and the average pore size of 8–13 nm, that is favorable for application as support for catalysts. Cr2O3/Al-Al2O3 catalysts had high activity and selectivity in dehydrogenation of n- and i-butane (conversion of 44–80 mol.% and selectivity >85% at temperatures of 540–610 °C), that is comparable ones for commercial catalysts for CATOFIN, STAR processes

Bimetallic PdAg nanoparticle arrays from monolayer films of diblock copolymer micelles

International audienceThe self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O-2 plasma and after hydrazine reduction