The catalytic performance of the non-purified MoVNbTeO x catalyst was optimized by changing the composition of the synthesis gel method in the hydrothermal synthesis process. However, the enhancement in activity was more pronounced for the post-treatment process of the non-purified catalyst. The catalytic performance of non-purified MoVNbTeO x catalysts and phase-pure M1 catalysts in the oxidative dehydrogenation of ethane (ODHE) were enhanced by water agitation post-treatment. The results showed that the phase-pure M1 catalyst obtained by treating the MoVNbTeO x catalyst with nitric acid had an increased activity per unit mass, but with a mass loss of catalyst materials during the purification process. After several days of post-treatment with water agitation, the catalytic activity of the non-purified MoVNbTeO x and the M1 samples gradually increased and stabilized, where both catalysts had a comparable catalytic performance. All the samples were systematically characterized, showing that the catalytic performance of the samples was mainly correlated with the enhanced specific surface area/pore volume. The results show that for the hydrothermally synthesized MoVNbTeO x catalysts, the reaction takes place in the micropores and the key to improve the performance of MoVNbTeO x catalysts is to effectively expose the active sites. Physical post-treatment process that does not require nitric acid or hydrogen peroxide for purification is also effective in enhancing catalyst activity by boosting the active site.
MoVNbTeO x is the most promising catalyst for the oxidative dehydrogenation of ethane (ODHE) process, which is usually prepared by hydrothermal methods. However, the synthesis of MoVNbTeO x is time-consuming and sensitive to the homogeneity of the synthesis environment, which limits its preparation reproducibility and large-scale accessibility. In this work, a continuous flow hydrothermal synthesis (CFHTS) process for the preparation of MoVNbTeO x catalysts was developed and the synthesis parameters were screened using a tubular reactor. Using a micro coil tube as a reactor, MoVNbTeO x catalysts can be synthesized rapidly at 300 °C and 10 MPa. Meanwhile, the catalytic performance of MoVNbTeO x synthesized by CFHTS method was also significantly improved, with the activity nearly doubled compared to the samples prepared by the conventional method. Compared with the conventional method, the preparation time of CFHTS method can be shortened from 48 h in the batch mode to 10 min in the continuous mode, and the capacity per unit volume of the reactor has been increased by orders of magnitude, which provides the possibility of industrial scale-up of MoVNbTeO x catalysts.
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