Abstract
This work provides an innovative method for preparing different isomerization catalysts by impregnating different proportions of MgCl2 and AlCl3 and combining different K compounds on cellulose-derived biochar, followed by pyrolysis. Results show MgO and Al(OH)3 existing in 4Mg-1Al-C catalyst can obtain better catalytic effect on glucose isomerization than the singe of Al presenting in 0Mg-1Al-C catalyst. Moreover, the synergism effects of the multi-catalytic active sites such as 帣-, 帠-Al(OH)3, KCl, MgO, and K4H2(CO3)3 in Mg-Al-KHCO3-C catalyst can further lead to an increase in glucose isomerization, compared to the 4Mg-1Al-C catalyst. The X-ray diffraction results present that the value of O/Al in Mg-Al-KHCO3-C catalyst is as high as 13.38, which provides many unsaturated acidic catalysis sites and benefits the glucose isomerization. Simultaneously, the TPD results reveal that the main active sites (MgO, Al(OH)3, and K4H2(CO3)3) in Mg-Al-KHCO3-C catalyst can provide weakly acidic and basic sites and avoid strongly acidic and basic sites to excessively attack the glucose. Based on the DFT analysis, the results indicate that the MgO has a great effect on the ring-opening reaction to form acyclic glucose, while Al(OH)3+ has a great effect on promoting acyclic glucose hydrogen transfer isomerized to form fructose. Compared to other carbon-based metal catalysts, the prepared Mg-Al-KHCO3-C has excellent catalytic performance, which gives a higher fructose yield (38.7%) and selectivity (87.72%) and glucose conversion (44.12%) at 100 簞C in 30 min. In this study, we develop a highly efficient Mg-Al-K-biochar catalyst for glucose isomerization and provide an efficient method for cellulose valorization.
