TY - JOUR

T1 - A Mechanistic Study of Dehydrogenation of Propane over Vanadia-Titania Catalysts

AU - Kaichev, Vasily V.

AU - Chesalov, Yuriy A.

AU - Saraev, Andrey A.

AU - Tsapina, Anna M.

PY - 2019/8/15

Y1 - 2019/8/15

N2 - The oxidative and non-oxidative dehydrogenation of propane over a monolayer V2O5/TiO2 catalyst was examined using in situ Fourier transform infrared spectroscopy and pseudo in situ X-ray photoelectron spectroscopy (XPS). It was found that the freshly calcined catalyst contains vanadium in the V5+ state; however, its treatment in the propane flow leads to the reduction of V5+ to V3+. Simultaneously, the catalyst treatment in propane leads to the formation of Ti-O-H groups, the removal of vanadyl oxygen species, and accumulation of carbonaceous deposits. Besides, XPS data indicate that the reduction of catalyst is accompanied by reversible destruction of the vanadia monolayer and formation of 3D clusters or nanoparticles on the titania surface, which leads to catalyst deactivation. In contrast, under the action of a propane/oxygen mixture flow, the accumulation of carbonaceous deposits and the destruction of the vanadia monolayer do not proceed. In this case, V5+ cations are partially reduced to V4+, and the catalyst surface contains isopropoxide, acetone, formate, acetate, and carbonate species. We suggest that the oxidative dehydrogenation of propane to propylene over vanadium oxide-based catalysts proceeds via the redox mechanism, where the oxidized catalyst surface oxidizes propane and is reoxidized by gas-phase oxygen. The active sites contain V5+ cations, and the C-H bond of propane is activated preferentially on vanadyl oxygen species. The key intermediate is isopropoxide, which can transform to propylene or acetone. Adsorbed acetone is unstable and oxidized further to formate and acetate species, which could be oxidized to CO and CO2. In contrast, the non-oxidative dehydrogenation of propane proceeds over the reduced catalyst. In this case, active sites contain V3+ cations. The mechanisms of both reactions are discussed.

AB - The oxidative and non-oxidative dehydrogenation of propane over a monolayer V2O5/TiO2 catalyst was examined using in situ Fourier transform infrared spectroscopy and pseudo in situ X-ray photoelectron spectroscopy (XPS). It was found that the freshly calcined catalyst contains vanadium in the V5+ state; however, its treatment in the propane flow leads to the reduction of V5+ to V3+. Simultaneously, the catalyst treatment in propane leads to the formation of Ti-O-H groups, the removal of vanadyl oxygen species, and accumulation of carbonaceous deposits. Besides, XPS data indicate that the reduction of catalyst is accompanied by reversible destruction of the vanadia monolayer and formation of 3D clusters or nanoparticles on the titania surface, which leads to catalyst deactivation. In contrast, under the action of a propane/oxygen mixture flow, the accumulation of carbonaceous deposits and the destruction of the vanadia monolayer do not proceed. In this case, V5+ cations are partially reduced to V4+, and the catalyst surface contains isopropoxide, acetone, formate, acetate, and carbonate species. We suggest that the oxidative dehydrogenation of propane to propylene over vanadium oxide-based catalysts proceeds via the redox mechanism, where the oxidized catalyst surface oxidizes propane and is reoxidized by gas-phase oxygen. The active sites contain V5+ cations, and the C-H bond of propane is activated preferentially on vanadyl oxygen species. The key intermediate is isopropoxide, which can transform to propylene or acetone. Adsorbed acetone is unstable and oxidized further to formate and acetate species, which could be oxidized to CO and CO2. In contrast, the non-oxidative dehydrogenation of propane proceeds over the reduced catalyst. In this case, active sites contain V3+ cations. The mechanisms of both reactions are discussed.

KW - DENSITY-FUNCTIONAL THEORY

KW - OXIDATIVE DEHYDROGENATION

KW - SELECTIVE OXIDATION

KW - ACTIVE-SITES

KW - FORMIC-ACID

KW - FT-IR

KW - OXIDE

KW - SURFACE

KW - SILICA

KW - ALKANES

UR - http://www.scopus.com/inward/record.url?scp=85070883538&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.9b04991

DO - 10.1021/acs.jpcc.9b04991

M3 - Article

AN - SCOPUS:85070883538

VL - 123

SP - 19668

EP - 19680

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 32

ER -