Abstract
Increasing demand for CO2 utilisation reactions and the stable character of CO2 have motivated interest in developing highly active, selective and stable catalysts. Among the materials which have comparatively low prices, transition metal carbides (TMCs) and transition metal phosphides (TMPs) catalysts exhibit high catalytic performance towards CO2 upgrading reactions and the research dealing with these two categories catalysts are relatively scarce. Under these premises, in this thesis, I have studied the design and application of TMCs and TMPs catalysts for chemical CO2 upgrading.
This thesis consists of one review chapter and five experimental chapters, four different series of TMCs or TMPs catalysts were synthesised and tested under the condition of each CO2 upgrading reactions. The third and fourth chapters explored the influence of promoters (Cu and Cs) on two TMCs catalysts (Mo2C and FexC) towards Reverse Water Gas Shift (RWGS) reaction. As for the Mo2C catalysts, this work showcases the Cs-promoted catalyst reaches 100% CO selectivity in the low-temperature range due to the electropositive character of Cs which facilitates the electronic transfer from Cs to Mo and leads to an electronically rich surface favouring the selectivity towards CO. Besides, the Cu/Cs-Mo2C catalysts also displayed catalytic activity for methanol synthesis (chapter7). As for the FexC catalysts, we found that the carburisation process was hindered when Cs and Cu are added to the Fe3C formulation. In addition, Fe/Fe5C2 are more active and selective for RWGS reaction than Fe3C.
The TMPs catalysts developed for this thesis (chapter5, chapter6) were NixP catalysts and MoP catalysts with different supports. This work reports for the first time the support dependent activity and selectivity of Ni-rich nickel phosphide catalysts for CO2 hydrogenation. Ni2P/SiO2 is a highly selective catalyst for RWGS, producing over 80% CO in the full temperature range of 350-750oC. When supported on Al2O3 or CeAl, the dominant phase of as-synthesised catalysts is Ni12P5 and these Ni12P5 catalysts show activity for methanation at low temperatures with a switchover to RWGS at higher temperatures. On the contrary, MoP catalysts show high selectivity for RWGS regardless of the supports.
Overall, this thesis is based on synthetic development and reactive studies to produce highly effective catalysts for CO2 upgrading reactions.