Support effects in vanadium incipient wetness impregnation for oxidative and non-oxidative propane dehydrogenation catalysis

Abstract

Oxidative propane dehydrogenation with carbon dioxide (OPDH) is an attractive technology, co-producing carbon monoxide and propylene with a potentially negative greenhouse gas balance. Vanadium oxide containing materials are a promising class of catalysts for such process. In this study, we introduce vanadium into a range of micro- and mesoporous aluminosilicate materials by incipient wetness impregnation with NH4VO3 and the complexing agent oxalic acid, targeting a surface density of 0.6 V atoms per nm² of pristine support. Aspects of this impregnation procedure and its interaction with the support are discussed in the context of potential sources of variability in the dispersion of VOx species within the catalyst materials. The results indicate no formation of a monolayer of vanadium species, and differences in catalyst dispersion are discernible through comprehensive characterization techniques, including thermogravimetric analysis (TGA), X-ray diffraction, Raman spectroscopy, H2-TPR and UV-Vis spectroscopy. The materials are evaluated for the catalytic CO2-assisted propane dehydrogenation in two pressure regimes while being compared to classic non-oxidative propane dehydrogenation (PDH). Results are analyzed using a multivariable analysis of reactants and products, which provided valuable insights for catalyst design. The larger pore material with few acid sites (MCM-41 with Si/Al = 180) demonstrates the highest activity in terms of PDH and high pressure OPDH, i.e. high propane conversion and quasi-equivalent propylene production with similar CO2 co-conversion and CO co-production). Yet, in terms of responding to the introduction of CO2, the zeolites seem to respond better in terms of producing less H2 for only a small decrease in propylene. These microporous materials, except for the most acidic aluminous BEA, exhibit a significant increase in their production rates when increasing the total pressure in OPDH.