Construction of New Active Sites: Cu Substitution Enabled Surface Frustrated Lewis Pairs over Calcium Hydroxyapatite for CO₂ Hydrogenation

Abstract

Calcium hydroxyphosphate, Ca 10 (PO 4 ) 6 (OH) 2 , is commonly known as hydroxyapatite (HAP). The acidic calcium and basic phosphate/hydroxide sites in HAP can be modified via isomorphous substitution of calcium and/or hydroxide ions to enable a cornucopia of catalyzed reactions. Herein, isomorphic substitution of Ca 2+ ions by Cu 2+ ions especially at very low levels of exchange created new analogs of molecular surface frustrated Lewis pairs (SFLPs) in Cu x Ca 10−x (PO 4 ) 6 (OH) 2 , thereby boosting its performance metrics in heterogeneous CO 2 photocatalytic hydrogenation. In situ Fourier transform infrared spectroscopy characterization and density functional theory calculations provided fundamental insights into the catalytically active SFLPs defined as proximal Lewis acidic Cu 2+ and Lewis basic OH − . The photocatalytic pathway proceeds through a formate reaction intermediate, which is generated by the reaction of CO 2 with heterolytically dissociated H 2 on the SFLPs. Given the wealth of information thus uncovered, it is highly likely that this work will spur the further development of similar classes of materials, leading to the advancement and, ultimately, large-scale application of photocatalytic CO 2 reduction technologies.

Phosphines Modulating the Catalytic Silane Activation on Nickel–Cobalt Nanoparticles, Tentatively Attributed to Frustrated Lewis Pairs in a Colloidal Solution

“…11 Recently, the group of Ozin used copper substitution in calcium hydroxyapatite to design a CO 2 hydrogenation catalyst. 12 All these solid heterogeneous catalysts, however, do not take benefit from the mobility of a molecular partner in solution, which can greatly increase the chances of identifying novel FLPs systems. In this context, we wanted to investigate the possibility of creating a FLP in colloidal solutions based on inorganic nanoparticles of abundant first row transition metals (the Lewis acid) and an external ligand (the Lewis base), free to come and go from the nanoparticle's surface.…”

“…11 Recently, the group of Ozin used copper substitution in calcium hydroxyapatite to design a CO 2 hydrogenation catalyst. 12 All of these solid heterogeneous catalysts, however, do not take benefit from the mobility of a molecular partner in solution, which can greatly increase the chances of identifying novel FLP systems.…”

“…Such phenomenon has been recently exploited by Qu et al, who reported the spectacular reactivity of a CeO 2 catalyst for the hydrogenation of olefins . Recently, the group of Ozin used copper substitution in calcium hydroxyapatite to design a CO 2 hydrogenation catalyst . All of these solid heterogeneous catalysts, however, do not take benefit from the mobility of a molecular partner in solution, which can greatly increase the chances of identifying novel FLP systems.…”

Photocatalytic Reduction of CO2 with H2O Mediated by Ce-Tailored Bismuth Oxybromide Surface Frustrated Lewis Pairs

“…The high-resolution XPS peaks for Ce-BiOBr exposed to a H 2 atmosphere at room temperature (Figure c,d) illustrate the slight movement to positive energy in the O 1s region, resulting from the formation of hydroxides due to the addition of H + , while the peaks of Ce 3d and Bi 4f show slight negative shifts, induced by the bonds of H – with Ce and Bi ions (Figure S17). These shifts could reflect the splitting of H 2 by the frustrated Lewis acid–base pair Ce 4+ -O 2– with protonation, evidently proving the FLP characteristics in Ce-BiOBr …”

“…The generation rates of CO and CH 4 over the BiOBr-OVs/C 3 N 4 heterojunction correspond to 13.8 and 6.1 μL h –1 , respectively, larger than that of the heterojunction C 3 N 4 /BiOBr without OVs . Our group reports that the products of CO 2 photoreduction for hollow BiOBr microspheres are dominated with CO and CH 4 in yields of 19.7 and 1.3 μL h –1 , showing 8.8 and 5.8 times as large as plate-like BiOBr, respectively . More recently, we showed that the PVP coordinated BiOBr has an excellent activity for CO 2 photoreduction with pure H 2 O under simulated sunlight.…”