Intrazeolite Anchoring of Co, Ru, and [Ru−Co] Carbonyl Clusters: Synthesis, Characterization, and Their Catalysis for CO Hydrogenation

Abstract

This paper focuses on the intrazeolite anchoring of Co, Ru, and Ru−Co carbonyl clusters and their catalytic performances for CO hydrogenation. The synthesis of intrazeolite anchoring of [HRuCo3(CO)9(μ2-CO)3] involves the adsorption of metal carbonyl species into zeolite cages followed by reductive carbonylation under a mixed CO and H2 atmosphere. The physicochemical characterization used a multianalytical approach, including FT-IR and EXAFS spectroscopies and CO/H2 gas chemisorption. The research concluded several key points as follows. (i) There is significant bimetallic interaction. (ii) The generation process of bimetallic carbonyl clusters was considered to occur through the interaction of [Ru−Co], Co(CO)4-, and RuI carbonyls, and conversion into [HRuCo3(CO)9(μ3-CO)3] and further to [HRuCo3(CO)9(μ2-CO)3] isomer. (iii) Internal and external confinement of [HRuCo3(CO)9(μ3-CO)3] were compared. (iv) The intrazeolite anchoring of [RuCo3] carbonyl clusters shows a strong reaction with the extraframework Na+ α-cage cations through involvement of the oxygen end of the bridging carbonyl ligands. (v) The bimetallic Ru−Co cluster catalyst shows higher CO conversion and oxygenates selectivity than the monometallic Co or Ru cluster. A high Co ratio in the Ru−Co cluster catalyst enhances the catalytic activity and the selectivity of oxygenates. (vi) The catalytic properities such as oxygenates selectivity depend on cluster size. Basic NaX is superion to NaY in enhancing oxygenates selectivity. (vii) Infrared spectra, 13CO, D2 isotopic exchange, and mass studies prove that a surface η2-formyl species adsorbed on Ru−Co interaction sites is an intermediate of oxygenate formation. The adjacent Ru−Co sites suppress η2-formyl adspecies dissociation and promote formyl species insertion into alkyl adspecies to enhance heavy oxygenate formation. (ix) The deactivated bimetallic Ru−Co cluster catalyst can be regenerated by hydrogen treatment, whereas the monometallic Co cluster catalyst cannot be regenerated.