Constructing A Rational Kinetic Model of the Selective Propane Oxidation Over A Mixed Metal Oxide Catalyst

Christoph Sprung,Gregory Yablonsky,Annette Trunschke,Robert Schlögl

doi:10.3390/catal8080330

Abstract

This research presents a kinetic investigation of the selective oxidation of propane to acrylic acid over a MoVTeNb oxide (M1 phase) catalyst. The paper contains both an overview of the related literature, and original results with a focus on kinetic aspects. Two types of kinetic experiments were performed in a plug flow reactor, observing (i) steady-state conditions (partial pressure variations) and (ii) the catalyst evolution as a function of time-on-stream. For this, the catalyst was treated in reducing atmosphere, before re-oxidising it. These observations in long term behaviour were used to distinguish different catalytic routes, namely for the formation of propene, acetic acid, acrylic acid, carbon monoxide and carbon dioxide. A partial carbon balance was introduced, which is a ‘kinetic fingerprint’, that distinguishes one type of active site from another. Furthermore, an ‘active site’ was found to consist of one or more ‘active centres’. A rational mechanism was developed based on the theory of graphs and includes two time scales belonging to (i) the catalytic cycle and (ii) the catalyst evolution. Several different types of active sites exist, at least as many, as kinetically independent product molecules are formed over a catalyst surface.

Highlights

Light alkenes are largely produced from crude oil feedstock by steam-cracking
The synthesis of maleic anhydride from butane has already been realised in larger scale, whereas the analogous selective oxidation of propane and ethane still faces challenges in their performance to compete with the established alkene-based processes [1,2]
X-ray fluorescence (XRF) investigations gave an element distribution of Mo/V/Te/Nb/O = 46.27%/6.74%/6.82%/7.01%/33.2%

Summary

Introduction

Light alkenes are largely produced from crude oil feedstock by steam-cracking. These hydrocarbons are transformed into valuable intermediates, such as ethylene oxide, acrylic acid, and maleic anhydride.Current research efforts are undertaken to establish alkanes instead of alkenes as feedstock for the latter processes, facilitating the change from a crude oil to natural gas-based economy in this respect.The synthesis of maleic anhydride from butane has already been realised in larger scale, whereas the analogous selective oxidation of propane and ethane still faces challenges in their performance to compete with the established alkene-based processes [1,2].For the complex reaction of propane oxidation on oxide catalysts, the MoVTeNbOx in the M1 structure, has been studied by many researchers under different conditions, including atmospheric conditions and high vacuum (cf. Table 1). Light alkenes are largely produced from crude oil feedstock by steam-cracking. These hydrocarbons are transformed into valuable intermediates, such as ethylene oxide, acrylic acid, and maleic anhydride. Current research efforts are undertaken to establish alkanes instead of alkenes as feedstock for the latter processes, facilitating the change from a crude oil to natural gas-based economy in this respect. The synthesis of maleic anhydride from butane has already been realised in larger scale, whereas the analogous selective oxidation of propane and ethane still faces challenges in their performance to compete with the established alkene-based processes [1,2]. For the complex reaction of propane oxidation on oxide catalysts, the MoVTeNbOx in the M1 structure, has been studied by many researchers under different conditions, including atmospheric conditions and high vacuum (cf Table 1)

Methods

Results

Discussion

Conclusion