Abstract
Direct selective oxidation of hydrocarbons to oxygenates by O2 is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C−H bonds at benzylic positions. In this work, stable, lead‐free, Cs3Bi2Br9 halide perovskites are integrated within the pore channels of mesoporous SBA‐15 silica and demonstrate their photocatalytic potentials for C−H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C5 to C16 including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol gcat −1 h−1 and excellent selectivity (>99 %) towards aldehydes and ketones under visible‐light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well‐dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp3)−H bond activation by photoinduced charges.
Highlights
The selective oxidation of sp3 CÀH bonds using O2 to valuable oxygenated products is one of the most important reactions in the chemical industry for fine chemicals and pharmaceuticals production.[1]
The halide perovskite Cs3Bi2Br9 nanoparticles were formed within the mesopores of SBA-15 silica with different loadings by the incipient wetness impregnation (IWI) method.[22]
When the loading is increased to 10 wt %, the high dispersion of small perovskite nanoparticles is still maintained as illustrated by Figure 1 c,d
Summary
The selective oxidation of sp CÀH bonds using O2 to valuable oxygenated products is one of the most important reactions in the chemical industry for fine chemicals and pharmaceuticals production.[1]. Among narrow-band gap semiconductor materials, allinorganic halide perovskites (ABX3 with A = Rb, Cs; B = Ge, Pb, Sn; and X = Cl, Br, I) have gained increasing attention owing to their unique photovoltaic and optoelectronic properties.[8] With the rapid growth in solar cells, many different novel research avenues on halide perovskites have emerged They are hardly explored in heterogeneous catalysis.[9] Following the first report using MAPbI3 for photocatalytic hydrogen evolution,[10] lately toxic lead-based perovskites (for example, CsPbBr3 and CsPbI3) have been used for photocatalytic reactions such as dye degradation,[11] CO2 reduction,[8b,12] and various organic transformations including C(sp3)ÀH bond activation,[7i] alcohol oxidation,[13] aldehyde alkylation,[14] thiol reaction,[15] CÀC cleavage, and dehydrogenation.[16] CsPbBr3 nanocrystals have successfully driven other organic synthesis such as CÀC, CÀO, and CÀN bond-forming reactions.[17] In comparison, cheap, low-toxic, and air-stable bismuth-based counterparts such as Cs3Bi2X9[18] and Cs2AgBiX6[19] showed a few applications in photocatalysis (CO2 reduction,[19e] ring-opening reactions,[20] and dye degradation[21]). By using toluene oxidation as a model reaction, our experimental, spectroscopic, and computational studies reveal that supported perovskite nanoparticles show enhanced charge separation and close interactions with hydrocarbons that promote CÀH bond activation
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