Prospects of Heterogeneous Hydroformylation with Supported Single Atom Catalysts

Abstract

The potential of oxide-supported rhodium single atom catalysts (SACs) for heterogeneous hydroformylation was investigated both theoretically and experimentally. Using high-level DLPNO-CCSD(T) calculations, both stability and catalytic activity were investigated for Rh single atoms on different oxide surfaces. Atomically dispersed, supported Rh-catalysts were synthesized on MgO and CeO2. While the CeO2-supported rhodium catalyst is found to be highly active, this is not the case for MgO, most likely due to increased confinement, as determined by EXAFS, that diminishes the reactivity of Rh complexes on MgO. This agrees well with our computational investigation, where we find that rhodium carbonyl hydride complexes on flat oxide surfaces such as CeO2( 111) have catalytic activities comparable to those of molecular complexes. For a step edge on a MgO(301) surface, however, calculations show a significantly reduced catalytic activity. At the same time, calculations predict that stronger adsorption at the higher coordinated adsorption site leads to a more stable catalyst. Keeping the balance between stability and activity appears to be the main challenge for oxide supported Rh hydroformylation catalysts. In addition to the chemical bonding between rhodium complex and support, the confinement experienced by the active site plays an important role for the catalytic activity.

Economizing on Precious Metals in Three‐Way Catalysts: Thermally Stable and Highly Active Single‐Atom Rhodium on Ceria for NO Abatement under Dry and Industrially Relevant Conditions**

“…Thereafter,wereacted it with D 2 ( Figure S21). In this case,similarly to Rh III (CO)H 2 on FAU, the CO band in the middle shifted to lower wavenumbers by approximately % 7-8 cm À1 ,a nalogous to the zeolite case.Thus we confirm that this CO band belongs to af amily of Rh III (CO)H 2 complexes and for the first time we show the formation of aR h-H complex on ceria which explains the reactivity of Rh 1 /CeO2 and Rh 1 /ZnO in hydroformylation reaction: [31,45] we trapped the catalytically important intermediate in our study and confirmed the feasibility of Rh-H species formation.…”

“…We also suggested the possibility of formation of Rh‐H species on Rh 1 /Ceria: we inferred this on the basis of ammonia formation in the presence of water. Interestingly, Rh 1 ions supported on ceria and zinc oxide were recently reported to be active species for heterogeneous hydroformylation reaction, although no Rh‐H intermediates were observed in those studies [31, 45] . For homogeneous hydroformylation, the active Rh species are Rh‐H species: however, they have never been observed on Rh/ceria or Rh/ZnO catalysts.…”

“…Interestingly, Rh 1 ions supported on ceria and zinc oxide were recently reported to be active species for heterogeneous hydroformylation reaction, although no Rh-H intermediates were observed in those studies. [31,45] Forhomogeneous hydroformylation, the active Rh species are Rh-H species:h owever,t hey have never been observed on Rh/ceria or Rh/ZnO catalysts. Not too long ago the first examples of well-defined and wellcharacterized carbonyl hydride complexes of at ransition metal belonging to the platinum group were reported.…”

Polymeric Heterogeneous Catalysts in the Hydroformylation of Unsaturated Compounds

“…For historical perspective, mention should be made of the scientifi c studies where different types of inorganic carriers such as silicon oxide [4][5][6][7], zeolites [8][9][10], and activated carbon [11,12] were used as materials for immobilization of metal complexes. The range of insoluble carriers used in the processes was considerably expanded thereafter, and at present the main metal fi xing methods include: incorporation of metal nanoparticles into the structures of various materials [13,18]; fi xing the rhodium complexes in the structure of the material by intercalation [19]; encapsulation of phosphine or a phosphine complex into mesopores or nanopores of the carrier [20,21]; the sol-gel method, "grafting" of a phosphine-containing hydrocarbon radical onto the carrier surface, and other methods of covalent bonding of phosphine fragments on an inorganic, hybrid or organic substrate, wherein rhodium is subsequently introduced [22][23][24][25][26][27][28]; fi xing of phosphine or a phosphine complex on the surface by means of ionic interactions [29]; fi xing of catalysts soluble in polar liquids (water and ionic liquid) in the thin hydrophilic layer of the carrier, which most frequently is silica gel SAPC/SIPC (Supported Aqueous/Ionic Liquid Phase Catalysts) [30,31]; creation of structures containing single rhodium atoms, as per the "single atom" concept [32], such as the cases in which nano-objects (nanosheets and nanofi bers) made of cobalt oxide [33] or zirconium oxide [34] were obtained and their catalytic properties were studied. Heterogeneous modifi ed rhodium clusters [35] and an iron-based catalyst [36] are also reported to have been used.…”

A Low Rhodium Content Smart Catalyst for Hydrogenation and Hydroformylation Reactions

“…In regard to the hydroformylation, even if this process is widely used in industry to synthesize many oxo-products with different fields of application, only few examples have been realized to this day using simple heterogeneous rhodium-based catalysts [15][16][17][18]. This reaction is usually carried out using catalytic complexes that work under homogeneous or biphasic conditions or are heterogeneously Fig.…”