A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy wit...A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Bronsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Bronsted to Lewis acid sites and high glucose conversion was observed over NbsW5 and NbTWs oxides with high ratios of Bronsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Bronsted acidity. The results indicate fast isom- erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Bronsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over NbTW3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb5W5 oxide.展开更多
TiO_(2) nanosheets with dominant{001}facets,coupled with Cs_(2.5)H_(0.5)PW_(12)O_(40),were successfully synthesized by a one-step hydrothermal reaction.The photocatalytic activity of nanocatalysts was evaluated by the...TiO_(2) nanosheets with dominant{001}facets,coupled with Cs_(2.5)H_(0.5)PW_(12)O_(40),were successfully synthesized by a one-step hydrothermal reaction.The photocatalytic activity of nanocatalysts was evaluated by the degradation of Rhodamine B under UV light irradiation.The results showed that both the addition of Cs_(2.5)H_(0.5)PW_(12)O_(40) and the exposed{001}facets of TiO_(2) have a positive effect on the photocatalytic activity.The improved photoactivity of nanocomposites in comparison with that of TiO_(2) nanosheets could be attributed to the synergistic effect between Cs_(2.5)H_(0.5)PW_(12)O_(40) and TiO_(2) which facilitates the separation of photo-induced hole-electron pairs.展开更多
文摘A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Bronsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Bronsted to Lewis acid sites and high glucose conversion was observed over NbsW5 and NbTWs oxides with high ratios of Bronsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Bronsted acidity. The results indicate fast isom- erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Bronsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over NbTW3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb5W5 oxide.
基金This work was supported by the National Natural Science Foundation of China(Nos.21371035,21173050).
文摘TiO_(2) nanosheets with dominant{001}facets,coupled with Cs_(2.5)H_(0.5)PW_(12)O_(40),were successfully synthesized by a one-step hydrothermal reaction.The photocatalytic activity of nanocatalysts was evaluated by the degradation of Rhodamine B under UV light irradiation.The results showed that both the addition of Cs_(2.5)H_(0.5)PW_(12)O_(40) and the exposed{001}facets of TiO_(2) have a positive effect on the photocatalytic activity.The improved photoactivity of nanocomposites in comparison with that of TiO_(2) nanosheets could be attributed to the synergistic effect between Cs_(2.5)H_(0.5)PW_(12)O_(40) and TiO_(2) which facilitates the separation of photo-induced hole-electron pairs.
