New Insights into the Key Role of Thermal Treatment in V/P/O Catalysts for the Selective Oxidation of n-Butane to Maleic Anhydride

TL;DR

This study shows how thermal treatment of vanadium-based catalysts can improve their ability to selectively convert n-butane to maleic anhydride.

Contribution

The study reveals how oxygen and water during thermal treatment influence the formation of active and selective V/P/O catalysts.

Findings

Oxygen is essential for forming vanadyl pyrophosphate and controlling vanadium oxidation state.

Water increases the crystallinity and conversion of vanadyl hydrogen phosphate to vanadyl pyrophosphate.

Higher P/V ratios in precursors lead to better MA selectivity under the same calcination conditions.

Abstract

This work explores the thermal treatment of V/P/O catalyst
precursors
to achieve active and selective catalysts for the oxidation of n-butane to maleic anhydride (MA) in a continuous-flow fixed-bed
reactor. Vanadyl pyrophosphate (V4+, VPP), the key catalyst
component, is produced together with suitable V5+ vanadium
orthophosphate (VOPO4) allotropic forms by thermally treating
vanadyl hydrogen phosphate hemihydrate (VHP) under various atmospheres
and temperature ramps. The characterization conducted by using X-ray
diffraction, Raman spectroscopy, and reaction testing allowed the
identification of optimal conditions for active and selective catalysts.
Oxygen is necessary for obtaining VPP and affects the vanadium oxidation
state, which is a crucial parameter for selectivity. Water enhances
the crystallinity and conversion of VHP to VPP. An optimized calcination
atmosphere (6:10:84 mol % O2/H2O/N2) ensures 70% MA selectivity at 50% butane conversion at 400 °C.
VHP precursors characterized by higher P/V ratios allow us to obtain
higher MA selectivity when treated under the same calcination conditions.
This study provides valuable insights into the VPP production steps,
representing the starting point for fine-tuning the calcination conditions
based on the VHP properties (i.e., P/V ratio and carbon content).

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