Isostructural Atomically Dispersed Rhodium Catalysts Supported on SAPO-37 and on HY Zeolite

Abstract

Zeolites are widely applied supports for metal catalysts, but molecular sieves with comparable structuressilicoalumino­phosphates (SAPOs)have drawn much less attention and been overlooked as supports for atomically dispersed metals. Now, we report SAPO-37 as a support for atomically dispersed rhodium in rhodium diethylene complexes, made by the reaction of Rh­(η2-C2H4)2­(acetyl­acetonate) with the support and anchored by two Rh–O bonds at framework tetrahedral sites, as shown by infrared and extended X-ray absorption fine structure spectra. The ethylene ligands were readily replaced with CO, giving sharp νCO bands indicating highly uniform supported species. A comparison of the spectra with those of comparable rhodium complexes on zeolite HY shows that the SAPO- and zeolite-supported complexes are isostructural, providing an unmatched opportunity for determining support effects in catalysis. The two catalysts had similar initial room-temperature activities per Rh atom for ethylene conversion in the presence of H2, but the SAPO-supported catalyst was selective for ethylene hydrogenation and the zeolite-supported catalyst selective for ethylene dimerization; correspondingly, the catalyst on the SAPO was more stable than that on the zeolite during operation in a flow reactor.

Characterization of a Metal–Organic Framework Zr6O8 Node-Supported Atomically Dispersed Iridium Catalyst for Ethylene Hydrogenation by X-ray Absorption Near-Edge Structure and Infrared Spectroscopies

“…The spectra give no evidence of bands characteristic of bridging CO ligands, which would have appeared at ∼1850 cm –1 and would have indicated the presence of iridium clusters . These results show that Ir­(CO) 2 groups had been installed on the MOF nodes, as expected. , …”

“…30 These results show that Ir(CO) 2 groups had been installed on the MOF nodes, as expected. 26,31 The MOFs UiO-66[H 2 BDC/AA], UiO-66[H 2 BDC-NH 2 / FA], and UiO-66[H 2 BDC-NO 2 /FA] were characterized by IR bands at 3685, 3686, and 3691 cm −1 (and a weak band characterizing UiO-66[H 2 BDC/AA] at 3780 cm −1 ), which have been assigned to terminal OH groups on the nodes (Figures S2, S6, and S7 in the Supporting Information). 25 Chemisorption of the iridium complex precursor on these MOFs led to the decreased intensity of these bands (Figures S2, S6, and S7 in the Supporting Information), implying that the precursor reacted with these groups, as it does with such groups on metal oxides.…”

“…11,25 One might anticipate that ν CO values would be the most informative when the metal carbonyls were bonded to well-defined (crystalline) supportsthose with nearly uniform sites, such as zeolites, as compared to less uniform materials, such as amorphous metal oxides. 1,42 Earlier work bears out this anticipation, 31,46,47 and, correspondingly, the carbonyl IR bands are sharper for the zeolite-supported metal carbonyls than the metal oxide-supported metal carbonyls, with full width at half maximum (fwhm) values providing a measure of uniformity of the bonding sites. 46 Our MOFs are clearly less nearly uniform as supports than zeolites (Table 4).…”

Bruce Gates: A Career in Catalysis

“…Gates et al extended the work in zeolite-supported mononuclear gold catalysts discussed above and synthesized a series of supported metal complexes and clusters using metal precursors bearing (acac) ligands. Zeolites and associated materials with larger pore apertures, such as HY, Beta, HSSZ-53, or SAPO-37, allow for facile mass transfer of metal precursors to acid sites inside zeolite crystals, exchanging acac ligands with the anionic oxygen ligands. − When the pore aperture of a zeolite is small relative to the size of a metal acac complex, it forms a mixture of physisorbed and chemisorbed metal complexes, yielding broad ν CO bands . In this case, EXAFS characterization provides only an average interatomic distance between metal and oxygen atoms.…”

Atomically Dispersed Pt-group Catalysts: Reactivity, Uniformity, Structural Evolution, and Paths to Increased Functionality

“…Detailed studies that have addressed the ideas mentioned above show that the local coordination of atomically dispersed Pt sites plays a key role in determining their reactivity. Supports can also participate with metal sites in reaction mechanisms either indirectly by dictating M–O coordination number and charge state (illustrated in Figure a) − or directly through Mars van Krevelen processes, , H-spillover, and vicinal acid site participation. , Developing mechanistic insights will continue to be important as catalysts with increased functionality and complexity are designed. Below, we suggest some pathways to increasing the functionality and performance of atomically dispersed metal catalysts.…”