Morphology of MoP catalyst under hydrogenation conditions: A DFT based thermodynamics study

Abstract

Hydrogen adsorption configurations and stable concentrations on a group of MoP surfaces [(001), (100), (101), (102), (110), (111), (112)] at different conditions have been theoretically investigated with DFT and atomistic thermodynamics methods. Our systematic studies suggest that dissociative H2 adsorption is favored on MoP catalyst, and the saturation coverage ranges from one to four monolayers (ML) on different surfaces. Additionally, the stable hydrogen concentration on each surface at any temperature and H2 partial pressure could be easily identified from the established equilibrium phase diagrams. Interestingly, hydrogen adsorptions modified the MoP surfaces stabilities, and eventually changed the morphologies of MoP nanoparticle. (100) and (101) surfaces are found to be most stable and dominant at wide ranges of temperatures and H2 partial pressures, which indicates their potentially key roles in determining catalytic properties of MoP catalyst. These findings agree reasonably with available experimental XRD and TEM measurements. Most importantly, the numbers and ratios of exposed surfaces on MoP nanoparticle could be adjusted by manipulating preparation temperatures and pressures. Our investigations provide essential information for selective synthesis of MoP catalyst with specific structures experimentally.