Methyl formate (MF) is an important chemical intermediate. The development of efficient catalysts for the synthesis of MF from methanol is of great significance to C1 chemistry. In this study,three composite catalysts supported by nanogold on silica carriers are designed and synthesized, including Schiff base-modified mesoporous silica/nanogold (Au-L@SiO2),microporous silica molecular sieve/nanogold (Au@S1),and amorphous silica/nanogold (Au δ+@SiO2). The experimental results show that the Au-L@SiO2 catalyst achieves 100% selectivity for the conversion of methanol to methyl formate at low temperature of 80 ℃,and its conversion rate is significantly better than that of the unmodified mesoporous Au@SiO2 catalyst,indicating that the unique chemical environment of nanogold in ligand-modified SiO2 helps to improve its catalytic activity. Compared with the above-mentioned microporous Au@S1 and mesoporous Au-L@SiO2 supported catalysts,amorphous Au δ+@SiO2 exhibits the highest catalytic activity,with a methanol conversion rate of 85% and a MF selectivity of 100%. To explain the mechanism of the high catalytic activity of Au δ+@SiO2,its local structure has been characterized by X-ray absorption fine structure spectroscopy (XAFS). The results show the presence of Au δ+ ionic in Au δ+@SiO2,indicating that gold ions are the key factor in enhancing its catalytic activity. In summary,this study shows that organic ligand modification and the construction of gold ion-type nano-gold catalysts play a key role in catalytic methanol oxidation. This provides a new strategy for the development of green and highly active nanocatalysts,and is of great significance for the industrial application of catalytic methanol to MF.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |