Contribution to MoO3-SiO2 and WO3-SiO2 utilization-active catalysts in jasmine aldehyde, 2-hexyl-1,3-dioxolane and methyllaurate synthesis

Several types of mixed molybdenum and tungsten oxide-SiO2 materials were prepared using sol-gel and wet impregnation method. In all cases, four different loading of MoO3 or WO3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy and its acidity was determined by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in three model reactions providing valuable fine chemicals-aldol condensation, acetalization and esterification. These reactions are usually catalyzed by homogenous catalysts. With increasing interest in environmental protection these catalysts are replaced by heterogeneous ones-offering easy separation from reaction mixture and a possibility of catalyst reuse. More specifically the chosen reactions were: aldol condensation of benzaldehyde with heptanal giving jasmine aldehyde (1), acetalization of heptanal by ethylene glycol giving 2-hexyl-1,3-dioxolane (2) and esterification of lauric acid by methanol giving methyllaurate (3). The prepared materials proved to be catalytically active in above mentioned reactions-in aldol condensation was the best result (78% heptanal conversion, 58% selectivity to jasmine aldehyde, 24 h) obtained using Mo 40 material prepared by impregnation. This material showed to be the best together with W 40 material prepared by sol-gel process in esterification (91 or 94% conversion, 24 h). Acetalization occurs very willingly, best results (heptanal conversion > 90% and selectivity > 90%, 5 h) was obtained using Mo and W 25 and 40 prepared by sol-gel and impregnation process.