CuO Nanoparticle-Decorated TiO₂-Nanotube Heterojunctions for Direct Synthesis of Methyl Formate via Photo-Oxidation of Methanol

Abstract

Methyl formate is widely employed as one of the important organic intermediates in C1 chemistry and as an environmentally benign chemical in the emerging area of “green chemistry”. We here study the catalytic effectiveness of CuO/TiO2-nanotube nanocomposites for the direct synthesis of methyl formate via methanol photo-oxidation in this paper. The CuO/TiO2-nanotube nanocomposites with 7% CuO weight loading give a promising photocatalytic performance (over 93.3% methanol conversion and 89.4% methyl formate selectivity) at 25 °C under 365 nm UV irradiation. The turnover frequency and the apparent quantum efficiency reach up to 22.9 molmethanol gcat –1 h–1 and 57.6% over 7% CuO/TiO2-nanotube, respectively, which is mainly because of the effective minimization of the recombination of photogenerated electrons and holes by the surface ultrasmall-sized CuO particles. Furthermore, these CuO/TiO2-nanotube nanocomposites exhibit excellent durability and robust nature during the catalytic processes of the methanol photo-oxidation to methyl formate. The experimental results demonstrate the promise of the robust CuO/TiO2 nanocomposites for efficient and green production of methyl formate, which may offer guidelines for the design of efficient catalysts for selective alcohol conversion to other valuable chemicals.

Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances

“…Copper oxide/titanium oxide composites are typical examples of p-n junction heterostructures. The CuO-TiO 2 was reported as a photocatalyst of organic compounds degradation [ 168 , 169 , 170 ], photoelectrocatalyst of water splitting [ 171 , 172 ] and carbon dioxide reduction [ 173 ]. Copper and titanium oxides have multiple roles in composite.…”

“…An electric field between the positive and negative ion cores is called a depletion region and the presence of this effect is facilitating the charge separation between electrons and holes [ 171 ]. Furthermore, the presence of copper oxide in titanium material extends the range of light absorption [ 170 ], acts as a cocatalyst [ 169 ] and can affect the reaction mechanism [ 173 ]. General mechanism of photoactivity of the CuO-TiO 2 composite is based on the transfer of photoinduced electrons from the conduction band of TiO 2 to the conduction band of CuO.…”

Recent Advances in Aerobic Photo-Oxidation over Small-Sized IB Metal Nanoparticles

“…The synergistic effects and unique electronic structure were considered to be the main reasons for their superior catalytic activity. [26,34,35]. Royal Society of Chemistry, 2019.…”

Recent Advances in Aerobic Photo‐Oxidation of Methanol to Valuable Chemicals

“…An over 97 % conversion and 83 % selectivity were achieved over the CuO/TiO 2 ‐P under mild conditions (365 nm irradiation). Interestingly, the catalytic activity has a strong relationship with surface oxygen vacancy (O V ) species during the CuO/TiO 2 ‐P catalyzed reactions, [62,63] Figure 6, indicating that the CuO nanoclusters can optimally tune excitons recombination through O V generation to promote the methanol conversions. Further, in‐situ attenuated total reflection infrared spectroscopic analysis reveals, for the first time, that the methanol oxidation most likely occurs via the pathway from the adsorbed methoxy (CH 3 O*) to adsorbed formaldehyde (CHO*) species, Figure 7.…”

“…While the oxygen is dissociated on CuO particles with the photo‐generated electrons and then to refill TiO 2 oxygen vacancies. The two processes are the rate‐determining steps for the photo‐oxidation reactions [62,63] . The HCHO* species quickly reacts with a neighboring CH 3 O* to give MF product.…”