Effect of VO_x Species and Support on Coke Formation and Catalyst Stability in Nonoxidative Propane Dehydrogenation

Abstract

VOx/SiO2–Al2O3 catalysts were prepared by grafting vanadyl acetylacetonate onto the supports with a SiO2 content between 0 and 100 wt. %. The degree of polymerization of VOx species and acidity both of pristine supports and the catalysts were evaluated. To determine their on‐stream stability and carbon deposition activity in nonoxidative propane dehydrogenation, continuous‐flow tests and in situ thermogravimetric measurements were performed. The rate constants of catalyst deactivation and carbon deposition were derived from kinetic evaluation of these experiments. Gathered experimental evidence pointed out that VOx species were significantly more active for coke formation than acid sites of the supports. The rate constant of carbon formation was found to increase with the degree of polymerization of VOx species, whereas no correlation between catalyst acidity and the rate constants of coking or deactivation could be drawn.

VOx/γ‐Al2O3 Catalysts for Propane Dehydrogenation Prepared by “Impregnation‐Solid Phase Reaction” Method with Aluminum Hydroxide as Support Precursor

“…However, most catalysts were prepared by impregnating vanadium‐containing solution on an available alumina and subsequent calcination process. The introduced VO x species usually decrease the specific surface area of the resulted catalysts ,. This phenomenon can be observed not only on alumina, but also on other supports, like SiO 2 –Al 2 O 3 , MCM‐41, MSU‐1 .…”

“…Alumina, as a frequently used support with stable structure and high specific surface area, has been widely used to prepare catalysts ,,. Vanadium oxide catalysts with porous alumina as support have been widely studied in the dehydrogenation of C 3 –C 4 alkanes ,,. However, most catalysts were prepared by impregnating vanadium‐containing solution on an available alumina and subsequent calcination process.…”

Nature of the Active Sites of VOx/Al2O3 Catalysts for Propane Dehydrogenation

“…As expected, with increasing metal loading, the edge energy decreased from 3.9 eV to 2.5 eV, indicating the increase in polymerization degree and the growth in domain size of vanadium oxides. [29][30][31] Previous studies have suggested that monovanadates, polyvanadate and V 2 O 5 formed at different vanadium densities:…”

“…4,29 In Figure 6a, carbonaceous material was 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 14 observed covering the 12V/Al catalyst after 4 h-PDH reaction, and the amount of coke deposition (i.e., 0.054 g/g cat ) was measure by TGA (Figure 6b). …”

Catalytic Behavior of Chromium Oxide Supported on Nanocasting-Prepared Mesoporous Alumina in Dehydrogenation of Propane

“…Many other promising catalytic systems that are less hazardous for the environment than chromium or cheaper than platinum are being investigated, and are based on vanadium [10,11,12], gallium [13,14], iron [15,16], tungsten [17] or indium [18] oxides. In most cases, catalytically active compounds are deposited on supports characterized by a large specific surface area and accessible pore system.…”