Ni-N synergy enhanced the synthesis of formic acid via CO2 hydrogenation under mild conditions

The direct CO(2 )hydrogenation to formic acid is appealing since it is a potential hydrogen storage material and can be a precursor of higher value-added products. Due to thermodynamic limitations, developing an efficient catalyst system for this process is quite a challenge. Herein, a Ni-based N-modified TiO2-supported catalyst that showed exemplary activity and selectivity toward formic acid synthesis (757 TON), which was reported to be the highest over noble metal-free catalyst system, is designed. The combined impact of Ni and N over TiO2 as a support was thoroughly investigated in this research for improved activity in the selective conversion of CO2 to formic acid. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigations showed direct coordination between Ni and N, which emphasizes the metal support interaction for significantly higher catalytic activity. In-depth characterization of Ni/ N-TiO2 reveals that CO2 undergoes insertion reaction with H-2 to yield formic acid on Ni0 as an active surface via the formate intermediate. Complementary DFT studies elucidate the pivotal effect of nitrogen doping on the TiO2 surface, which provides a more feasible pathway than pure TiO2 by lowering the activation barriers. More significantly, the catalyst demonstrated a steady performance in experiments involving continuous recycling and long-term study.

Automated summary

In this study, a Ni-based N-modified TiO2-supported catalyst was designed for the direct CO2 hydrogenation to formic acid, exhibiting excellent activity, selectivity, and stability. Investigations on X-ray photoelectron spectroscopy and X-ray absorption spectroscopy confirmed the direct coordination between Ni and N, while DFT studies revealed the crucial effect of nitrogen doping on the TiO2 surface.