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 [HRuCo 3 (CO) 9 (µ 2 -CO) 3 ] involves the adsorption of metal carbonyl species into zeolite cages followed by reductive carbonylation under a mixed CO and H 2 atmosphere. The physicochemical characterization used a multianalytical approach, including FT-IR and EXAFS spectroscopies and CO/H 2 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 Ru I carbonyls, and conversion into [HRuCo 3 (CO) 9 (µ 3 -CO) 3 ] and further to [HRuCo 3 (CO) 9 (µ 2 -CO) 3 ] isomer. (iii) Internal and external confinement of [HRuCo 3 (CO) 9 (µ 3 -CO) 3 ] were compared. (iv) The intrazeolite anchoring of [RuCo 3 ] carbonyl clusters shows a strong reaction with the extraframework Na + R-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, 13 CO, D 2 isotopic exchange, and mass studies prove that a surface η 2 -formyl species adsorbed on Ru-Co interaction sites is an intermediate of oxygenate formation. The adjacent Ru-Co sites suppress η 2 -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.

The Application of Zeolites and Periodic Mesoporous Silicas in the Catalytic Conversion of Synthesis Gas

“…Table 3 collects the catalytic behaviour of these faujasite-supported monometallic (Co or Ru) and bimetallic (Co-Ru) clusters in the CO hydrogenation at 275°C and 5 bar. As observed, the bimetallic catalysts, specially that with a Co/Ru atomic ratio of 3, display higher catalytic activity (up to 17-fold) and, interestingly, enhanced selectivity towards alcohols than the monometallic systems which are meaningfully less active and selective [91]. Additionally, unpromoted Rh/NaY catalysts can form Rh carbonyl clusters under reaction conditions (250°C, 100 bar, H 2 /CO = 1) which display high selectivity to acetic acid (up to 40%) at CO conversions below 2% [92].…”

“…1% [90]. Bimetallic Ru-Co clusters entrapped in faujasite zeolites (NaX and NaY) have also been shown to display unique properties due to synergetic effects, differing markedly from the catalytic behaviour of the corresponding monometallic clusters [91]. Table 3 collects the catalytic behaviour of these faujasite-supported monometallic (Co or Ru) and bimetallic (Co-Ru) clusters in the CO hydrogenation at 275°C and 5 bar.…”

Advanced Catalysts Based on Micro‐ and Mesoporous Molecular Sieves for the Conversion of Natural Gas to Fuels and Chemicals

“…Shen and Ichikawa showed that the composition of the metal clusters significantly determines the catalytic selectivity in the hydrogenation of CO [152]. They found a synergetic behavior, which boosts the selectivity to higher oxygenates, principally ethanol, for bimetallic Ru x Co y /NaY catalysts as compared to the monometallic counterparts, which produce mainly hydrocarbons.…”

Intrazeolite CO Methanation by Small Ruthenium Carbonyl Complexes: Translation from Free Clusters into the Cage

“…First attempts to synthesize such Ru based materials (Ru/ NaY) have already been reported in 1980 indicating the formation of Ru carbonyl clusters comprising at least three Ru atoms. [8] However, only fifteen years later Shen et al reported a "ship-in-a-bottle" synthesis of ruthenium carbonyl and hydrido carbonyl complexes such as Ru 3 (CO) 12 , Ru 4 (CO) 12 H 4 , Ru 6 (CO) 18 2À , and Ru 6 (CO) 18 H À inside the faujasite cages of Na 56 Y and Na 56 X zeolites. [9] Detailed structural analysis of the synthesized material revealed the anchoring of the Ru carbonyls via a strong interaction between the Na + cations of the zeolite and the CO molecules.…”

“…This barrier is associated with the transfer of the terminally bound hydrogen atom to a neighboring carbon atom and leads to the formation of a formyl intermediate. Although this reaction step appears to be endothermic by ΔE BD = 0.97 eV, the formation of a formyl-type intermediate has experimentally been shown to be feasible e. g. in the oxygenate formation from CO and H 2 on bimetallic ruthenium-cobalt (RuCo 3 ) carbonyl complexes embedded in Na 56 Y [18] as well as in the CO methanation on small ruthenium . The bands around 2000 cm À 1 are characteristic for the C=O stretch motion, the bands around 1000 cm À 1 correspond to motions of the zeolite framework, and the bands below 600 cm À 1 contain contributions from the CO ligands, the SiO zeolite framework as well as the Ru cluster core (< 300 cm À 1 ).…”