Abstract
The direct oxidation of low-concentration methane to value-added chemicals can not only reduce carbon emission but also provide an alternative production route for fossil fuels. Herein, we proposed a novel catalyst for the direct oxidation of low-concentration methane to methanol via the impregnation method, which selected copper and zinc as co-modifiers to modify the MOR catalyst. The highest methanol yield of 71.35 μmol·g(cat)(-1)·h(-1) was obtained over a bimetallic Cu(0.5)Zn(0.35)-MOR catalyst. The catalyst retained good activity after three cycles of testing experiments, indicating good recyclability. Based on the results of performance tests and characterization studies, it was confirmed that Cu species bound to the zeolite framework were the main active sites for methane oxidation. The introduction of Zn decreased the generation of the octahedrally coordinated extra-framework aluminum, which promoted the dispersion of Cu within the zeolite framework. In other words, more tetrahedrally coordinated FAl-stabilized Cu species were presented in our CuZn-MOR catalyst system in comparison to the monometallic Cu-MOR catalyst. Benefiting from the aforementioned modification, the agglomerative sintering of the metal during the reaction was effectively prevented. This work may provide a feasible guide for the future optimization of Cu-based catalysts designed for the selective oxidation of methane.