Catalytic Dehydrogenation of Methane to Hydrogen and Carbon Nanostructures with Fe-Mo Bimetallic Catalysts

Abstract

As a pathway to green hydrogen, the catalytic dehydrogenation of methane is an economical and COx-free alternative to produce sufficient volumes of hydrogen to address energy sustainability. This work attempts to develop a catalyst to enhance conversion, stability, and favorable carbon nanostructures. Monometallic Fe catalysts were synthesized on a mesoporous carbon template to identify the best catalyst synthesis methodology covering incipient wetness, hydrothermal, and wet impregnation methods. As a logical step to enhance the conversion, stability, and ease of separation of the catalyst from the product carbon, a bimetallic Fe-Mo was synthesized on the same mesoporous carbon template for the first time, using the hydrothermal method, by varying the Mo loading from 2.5 to 15%. The optimal catalyst design had a composition of 30%Fe-5%Mo with a specific surface area of 606.9 g/m2, offering the highest conversion and stability, at a temperature of 950 °C. The highest conversion corresponded to the lowest space velocity, highest reaction temperature, and highest CH4 concentration, with a maximum conversion of 90% and being stable until the end of 2 h of reaction time. X-ray diffraction analysis revealed the presence of Fe2O3 and mixed oxides, Fe2(MoO4)3 and FeMoO4 in the bimetallic catalyst. The initial H2 yield was ∼61%, and it decreased during the reaction, reaching 48% after 4 h of reaction. Various structural, textural, and morphological characterizations of the catalyst pre- and postreaction were performed using advanced analytical techniques. Graphitic carbon, an Fe-Mo alloy, and FeMoO4 phases were observed by XRD patterns of the spent catalyst. Carbon depositions with varying morphologies were observed under different reaction conditions ranging from carbon nanoparticles and carbon nanotubes to agglomerates of nanoparticles and nanoflowers. A well-defined network of carbon nanoflowers along with bamboo-shaped carbon nanotubes could be observed over the surface of the best catalyst under the optimized reaction conditions.