Creation of Mo active sites on indium oxide microrods for photocatalytic amino acid production

Abstract

As an n-type semiconductor, In 2 O 3 is considered a promising photocatalyst for producing amino acids using biomass derivatives as precursors. However, similar to other intrinsic semiconductors, In 2 O 3 suffers from poor charge dynamics. Herein, we show the synthesis of Mo-doped In 2 O 3 (Mo-In 2 O 3 ) with a porous rod-shaped structure through a onestep solvothermal reaction followed by calcination. Under visible-light irradiation, Mo-In 2 O 3 achieves a high conversion rate of 81% for the reaction that transforms lactic acid into alanine with a selectivity of 91%. Spectroscopic techniques and density functional theory calculations reveal that Mo doping introduces defect states slightly below the conduction band of In 2 O 3 , which improves the separation of photogenerated electron-hole pairs. In addition, Mo atoms on the surface form extra adsorption and reaction centers that greatly enhance the reaction rate. This work provides insights into the development of transition metal-doped semiconductor photocatalysts to produce amino acids.

Atomic Ruthenium‐Promoted Cadmium Sulfide for Photocatalytic Production of Amino Acids from Biomass Derivatives

“…When compared to the representative photocatalytic systems, [9,10] Ru 1 /CdS predominates in terms of conversion, selectivity, yield, and alanine formation rates (Figure 3d). The activity of the Mo‐In 2 O 3 catalyst [11] was close to that of Ru 1 /CdS, but the system used toxic N,N‐dimethylformamide (DMF) as a solvent and the reaction was carried out at low reactant concentrations (the ratio of lactic acid to catalyst is 18 : 1, which is about 1/8 of this work). Although the thermocatalytic system showed higher conversion of lactic acid and yield of alanine formation, [6b] the reaction rate (2.4 mmol Ala ⋅ g cat −1 ⋅ h −1 ) was only about 1/20 of that of Ru 1 /CdS and it requires high temperature (220 °C) and pressure of H 2 (1 MPa), thus highlighting the superiority of our system (Table S1).…”

“…[10] Jiang et al recently synthesized Mo-doped In 2 O 3 micro rods using an indium-containing metal-organic framework (MIL-68) as the structural directing template, which showed a higher rate of alanine formation up to 36.8 mmol Ala • g cat À 1 • h À 1 , while the reaction mechanism remains unexplored. [11] Since the pioneering work of Zhang et al in 2011, [12] single-atom catalysts (SAC) have emerged as a powerful class of catalysts with unique properties (e.g., uniform active sites, theoretical 100 % atomic utilization) compared to the traditional homo-and heterogeneous catalysts, and present exciting activity and selectivity in many catalytic reactions including hydrogenation, [13] Suzuki coupling, [14] photo-(electron)catalytic hydrogen evolution, [15] CO 2 reduction, [16] nitrogen fixation, [17] and transfer hydrogenation. [18] Recently, Li's group reported that atomically dispersed Pt on CdS selectively produced α-keto acids from α-hydroxy acids via oxidation reactions, while Pt nanoparticles on CdS switch the product selectively to CÀ C coupling reactions to produce tartaric acid derivatives.…”

“…Jiang et al. recently synthesized Mo‐doped In 2 O 3 micro rods using an indium‐containing metal–organic framework (MIL‐68) as the structural directing template, which showed a higher rate of alanine formation up to 36.8 mmol Ala ⋅ g cat −1 ⋅ h −1 , while the reaction mechanism remains unexplored [11] . Since the pioneering work of Zhang et al.…”

Heterogeneous photocatalysis for biomass valorization to organic acids

“…the conversion of LA to alanine with a conversion rate and reaction rate of 0.407 mmol h −1 and 0.369 mmol h −1 , respectively. 92 Doping of Mo enhances bulk and interfacial charge transfer, whilst forming Mo-O-In bonds as new active sites due to replacing In 3+ of the In 2 O 3 lattice with Mo 5+ . 92 In short, the activity of the reaction can be improved by altering the local electronic environment, enhancing the efficiency of photocarrier migration, and establishing new reactive sites.…”

“…Zheng et al reported the use of Mo-doped indium trioxide (Mo-In 2 O 3 ) as a photocatalyst for the conversion of LA to alanine with a conversion rate and reaction rate of 0.407 mmol h −1 and 0.369 mmol h −1 , respectively. 92 Doping of Mo enhances bulk and interfacial charge transfer, whilst forming Mo–O–In bonds as new active sites due to replacing In 3+ of the In 2 O 3 lattice with Mo 5+ . 92 In short, the activity of the reaction can be improved by altering the local electronic environment, enhancing the efficiency of photocarrier migration, and establishing new reactive sites.…”