Abstract
Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).
Highlights
The paths to sustainable development lead, inter alia, to the processing of raw materials from renewable resources into useful value-added products
One can postulate that both the strength of BAS and the proximity of LAS and BAS on the surface of Nb-25/SBA-15 can contribute to the highest activity and selectivity to acrolein in glycerol dehydration
The presented results have pointed out a significant difference in the niobium acidbase properties depending on the metal location in the SBA-15 ordered mesoporous silica
Summary
The paths to sustainable development lead, inter alia, to the processing of raw materials from renewable resources into useful value-added products Acrolein is a versatile intermediate that is largely employed in the chemical industry, among others, for the production of acrylic acid. In the catalytic production of acrylic acid via one pot oxidehydration process, in the first step, acrolein is formed in the presence of acidic centers on the catalyst surface, and redox centers are involved in the oxidation of acrolein to acrylic acid In both reactions, the dehydration and oxidehydration of glycerol, one of the most important causes of the solid catalyst deactivation is the formation of a coke deposit, for which the acidic centers involved in the first step of the reaction are mainly responsible. The search for minimization of coke formation in dehydration of glycerol is still an important task
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
