Ca–Ag compounds in ethylene epoxidation reaction

Abstract

The ethylene epoxidation is a challenging catalytic process, and development of active and selective catalyst requires profound understanding of its chemical behaviour under reaction conditions. The systematic study on intermetallic compounds in the Ca-Ag system under ethylene epoxidation conditions clearly shows that the character of the oxidation processes on the surface originates from the atomic interactions in the pristine compound. The Ag-rich compounds Ca 2 Ag 7 and CaAg 2 undergo oxidation towards fcc Ag and a complex Ca-based support, whereas equiatomic CaAg and the Ca-rich compounds Ca 5 Ag 3 and Ca 3 Ag in bulk remain stable under harsh ethylene epoxidation conditions. For the latter presence of water vapour in the gas stream leads to noticeable corrosion. Combining the experimental results with the chemical bonding analysis and first-principles calculations, the relationships among the chemical nature of the compounds, their reactivity and catalytic performance towards epoxidation of ethylene are investigated.

Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges

“…While this cannot be explained by the chemical potential, quantum chemical calculations showed that the strong adsorption of ethylene on the intermetallic surfaces hinders oxidation, thus stabilising the surface against the reactive atmosphere. As expected, this behaviour is not isotropic and a contribution gives all the details of this interesting interplay[ 123 ].…”

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

“…For example, for Pd 3 Zr, the surface Zr no longer retains its metallic state, even in the presence of parts per billion levels of oxygen . In this context, it is generally difficult to use alloys containing alkali or alkaline-earth − metals as catalysts while retaining their surfaces in their original metallic state.…”

Superior catalytic performance of intermetallic CaPt2 nanoparticles supported on titanium group oxides in hydrogenation of ketones to alcohols

“…In previous studies, intermetallic CaAg 2 was reportedly an attractive catalyst in ethylene epoxidation. 30 Therefore, we expected to obtain valuable insights regarding catalytic applicability from the prepared CaPt 2 catalysts. A commercial carbon catalyst with 3 wt% Pt was used as a reference catalyst to evaluate the alloying effect of Pt with Ca on hydrogenation performance.…”