Design and Fundamental Understanding of Novel Catalysts for Efficient Transformations of Shale Gas Components

Abstract

In recent years, due to the abundant storage and development of hydraulic techniques, studies relating to the inexpensive shale gas source have drawn increasing attention among both academic and industrial researchers. Besides the utilization in heating and electricity of ordinary life, the more important application of shale gas is to be used as the raw carbon source in the chemical industry. As a chemical feedstock, it can be converted to various value-added intermediates, such as oxygenates, olefins and heavy hydrocarbons, via distinct catalytic processes. In this dissertation, there are five significant catalytic processes discussed in detail, including the one-step production of acetic acid by coupling methane with carbon monoxide and oxygen under mild conditions, the complete oxidation of methane at relatively low temperature, the oxidation of ethane to form carboxylic acids (acetic acid and formic acid) at near room temperature and near ambient pressure, the stable dehydrogenation of ethane to produce ethylene, and the synthesis of formic acid directly from carbon monoxide at low temperature. To improve the efficiency of these catalytic transformations, the design of novel catalysts exhibiting good activity of the activation of methane or ethane and high selectivity of the ideal product is the key. Thus, a variety of novel catalysts were prepared through different synthetic methodologies and were used in these catalytic transformations of short-chain alkanes. Specifically, the singly dispersed rhodium atoms anchored in microporous aluminosilicate materials were employed for the effective conversion of methane and ethane into acetic acid that is one of the most significant chemical materials due to its wide applications. In addition, the coordination-number dependent nickel oxide catalysts were applied in the complete oxidation of methane at relatively low temperatures. Moreover, Pd promoted Zn-based catalysts were used for the enhancement of activity and stability of the production of olefin from ethane dehydrogenation. Furthermore, the new type of the zeolitic material - nanosheet FAU catalysts, synthesized by using the graphene oxide with confined spaces as a special template, were utilized to produce formic acid from carbon monoxide, which could be formed from methane, reacting with water at low temperature. As these proposed catalysts presented good performances of the listed catalytic transformations, it is essential to know how these catalysts activate methane or ethane and convert them into ideal products. In this dissertation, fundamental understandings of authentic structures of synthesized catalysts at an atomic level were obtained by using the multiple ex-situ and in-situ characterization techniques. Through the integration of the fundamental understanding of local structures of these catalysts under catalytic conditions and the experimental explorations of their catalytic performances, the correlation between the structure of catalysts and their activities can be built. The establishment of such intrinsic structure-activity correlation is meaningful for the advances of new types of catalysts in science and is beneficial to the future realization of feasible processes. To conclude, investigations in this dissertation demonstrated the design and fundamental understanding of novel catalysts for efficient transformations of shale gas components under relatively mild conditions. The applied methodologies and achieved results in these studies will provide insights into both essential studies and practical processes involving the activation and conversion of light hydrocarbons (methane and ethane).