Performance of phase-pure M1 MoVNbTeOx catalysts by hydrothermal synthesis with different post-treatments for the oxidative dehydrogenation of ethane

Phase-pure M1 catalysts with different post-treatments have been prepared from the same precursor slurry by hydrothermal synthesis and used to study the key factors influencing their performance in the oxidative dehydrogenation of ethane (ODHE) process. Different purification processes (i.e. steam treatment and hydrogen peroxide treatment) result in different tellurium (Te) contents and V5+ concentration in the catalysts. Catalytic tests reveal that there is a direct correlation between the amount of V5+ present in the catalysts and the catalytic activity. A hydrogen peroxide treatment increases the V5+ concentration and decreases the Te content which can improve the catalytic activity and stability in comparison with the steam treatment. A post-treatment with oxalic acid improves the catalyst surface area (54 m(2)/g) but causes some vanadium leaching. The phase-pure M1 catalyst calcined at 650 degrees C and purified by H2O2 shows the best catalyst productivity of 0.77 kg(C2H4)/kg(cat)/h at 73% ethane conversion and 85% ethylene selectivity in ODHE process. The formation of reduced Te(0) aggregates blocking the active sites is identified as a main reason for catalyst deactivation. A low Te content favors a stable catalyst with less risk of Te aggregation. However, at harsh operating conditions (i.e. high oxygen concentration and high reactor temperature) the performance of phase-pure M1 catalysts with a low Te content can also reduce obviously due to the formation of a new (V, Nb)-substituted theta-Mo5O14 and MoO2 phases. (C) 2015 Elsevier B.V. All rights reserved.