Catalytic Cooperation via Spillover of Oxygen: Dehydration—Dehydrogenation of 2-Butanol over SnO₂—MoO₃ Catalysts

Abstract

Strong synergetic phenomena in the dehydration-dehydrogenation of sec-butyl alcohol were observed at very low temperature using mechanical mixtures of separately prepared SnO 2 and MoO 3 . The principal effects were an increase in conversion as well as increases in yields and selectivities for butene and methyl-ethyl ketone. Characterization of the solids before and after catalytic tests by X-ray Photoelectron Spectroscopy coupled with Transmission Electron Microscopy, Raman Spectroscopy and X-ray Diffraction analysis excluded the possibility of an in situ formation of a mixed oxide or mutual contamination. Attempts for preparing true mixed Sn/Mo oxides have been unsuccessful as predicted from the literature, and catalysts prepared by incipient decomposition of homogeneous precursor, which should exhibit maximum contamination, have exhibited much lower activities than the corresponding mechanical mixtures. Taking into account these and previous results with SnO 2 + Sb 2 O 4 and MoO 3 + Sb 2 O 4 mixtures, the origin of the observed synergy can be explained by a "Remote Control Mechanism" : SnO 2 acts as a donor of spillover oxygen species (Oso) and MoO 3 as an acceptor of Oso. The role of Oso is to create selective sites on MoO 3 and to protect them from deactivation.When synergetic effects are observed between two oxide phases in a selective oxidation reaction, the existence of a mixed phase or its in situ formation during the catalytic test is a common way to explain the observed improvement of 1 Please see Acknowledgments, page 345.

Structural Characterization of Tin and Molybdenum Oxides Thin Films Deposited by RGTO

“…Moreover, the sensitivity to a specific gas of SnO 2 -based sensors can be tuned by doping with different cations (see for example refs −5). It was shown that SnO 2 doped by Mo is sensitive to alcohol detection; it leaves almost unchanged the response to NO 2 , and it has a low response to CO . However, it is also reported that when mixed Mo−Sn oxides are formed, the response to CO increases .…”