Impact of pyrone group on H₂S catalytic oxidization

The surface functional group plays an important role in H₂S catalytic oxidization. However, the specific effect of each group species has seldom been investigated. For the first time, we revealed by experimental and theoretical methods that the pyrone group was the most valuable group. An increase in the pyrone-group amount obviously decreased the kinetic reaction order of H₂S catalytic oxidization. The catalyst with the largest amount of pyrone group (0.1321 mmol·g^-1) showed the lowest reaction order (0.5896) and activation energy (16.25 kJ·mol^-1). By comparison, a catalyst with 0.0008 mmol·g^-1 of pyrone group had a reaction order of just 1.1852 and an activation energy of 81.22 kJ·mol^-1. The contribution of pyrone content to the kinetic reaction order had a negative correlation coefficient of -8.0665, which was three and five times larger than that of the quinone (-2.5568) and acidic groups (-1.7454), respectively. Moreover, density functional theory calculations showed that the pyrone group had the lowest energy gap (0.156 eV), far less than that (1.921 eV) of the carboxyl group. After H₂S was adsorbed, the pyrone group had a Mulliken atomic charge of 0.510, which was larger than that (0.236) of the carboxyl group. In other words, the pyrone group showed the best ability to facilitate electron transfer. As a result, the catalyst with 0.1321 mmol·g^-1 of the pyrone group removed 100% of the H₂S (450 ppm). This amount was 42% higher than a catalyst with 0.0008 mmol·g^-1 of the pyrone group. The main results of this work help to explain the mechanism of carbon material in various types of catalysis.