Influence of the preparation conditions for catalysts CrOx/SiO2 on their efficiency in propane dehydrogenation in the presence CO2

Several sets of chromium oxide catalysts supported on silica gel were prepared by precipitation. The optimization of the preparation conditions can considerably enhance the activity and stability of the catalysts in propane dehydrogenation in the presence of CO2. The most stable systems with the chromium content <3 wt.% retain their initial activity after long-duration tests and regenerations. Introducing the active phase on the support in several steps makes it possible to enhance the stability of the samples with a high content of chromium (7 wt.%). It was found that with an increase in the acidity of a solution of chromium nitrate for catalyst preparation (pH from 3 to 1) the rate of their deactivation increases during the work. When the acidity of this solution decreases (pH from 3 to 5), the yield of propylene in propane dehydrogenation increases. As found by UV diffuse reflectance spectroscopy and X-ray diffraction analysis, the CrOx/SiO2 catalysts are characterized by the agglomeration of the chromium oxide phase during the work accompanied by a decrease in dispersion and specific activity. The degree of agglomeration increases with an increase in the chromium content.