Dehydrogenation of alkanes to alkenes using CO2 as mild oxidant; an attractive method of CO2 utilisation

CO2 reduction has drawn much attention globally in the development of new processes and technology for avoiding the impact of serious climate change. On the other hand, the fossil fuel as energy resources cannot be easily replaced in order to greatly reduce CO2 emission. CO2 utilisation has been widely investigated in many manufacture/industries areas. This chemical conversion of CO2 is not only adding value to the process of CO2 reduction but also has economic and environmental benefits. Using CO2 as a feedstock in the synthesis of high-demand chemicals in modern chemical industry would have a high economic value. However, due to the stability of CO2, a highly effective heterogeneous catalyst is required in order to provide pathways to the synthesis of important chemicals in this way. In this work, CrOx-based catalysts supported on ZrO2 have been developed and investigated for the dehydrogenation of propane using CO2 with various metal oxides (Zn, Mn, Ca) as promoters. In addition, a different catalyst preparation method the “one-pot synthesis” has been used to develop a more effective catalyst than those in which the metal is added to a support in a conventional way. Another exciting part of the work is the regeneration process of deactivated catalysts for recovering their catalytic ability, thus extending their catalytic lifetime. Based on this work, we show that the one-pot catalysts provide different catalyst surface morphologies, structures, and catalytic properties as compared to the conventional impregnation catalysts. The dominated ZrO2 species changed from monoclinic phase in the impregnation catalysts to tetragonal phase in one-pot catalysts. It also reveals a more uniform and highly dispersed catalytically CrOx active phase in which the CrOx species can be involved in the reaction more effectively than the corresponding impregnated catalysts. In addition, one-pot catalyst showed an increase amount of the active Cr(VI) species. The introduction of a CaO promoter, the catalyst shows different surface acidity and basicity. In addition, the 2Cr/Ca-ZrO2 shows an increase in both the overall propane conversion and propylene selectivity. The CaO promoter helps the process to reach 18% of propane conversion with 20% propylene yield and keep for 4-5 hours during the process. After the process, the propane conversion reduces to 10%, 15% product yield but with still about 93% propylene selectivity. Moreover, it also reduces the level of detrimental carbon deposition on the catalyst particles leading to enhanced stability and performance. In addition, the regeneration process can recover the catalytic ability for a continuous CO2-PDH process which shows the good potential for the long-term stable performance of the one-pot catalysts. The development of novel catalytic system for CO2-PDH make this process more attractive and effective not only in reducing net CO2 emission by using it to produce useful chemical products but also by helping reach the demand for these (propylene in this case). The work suggests that further development of catalysts for this and similar processes is desirable.

Keywords: propane dehydrogenation
metal catalyst
CO2
Advisor: Edwards, P
Clarke, S
Compton, R