Conversion of glucose to lactic acid derivatives with mesoporous Sn-MCM-41 and microporous titanosilicates

BACKGROUND: The production of value-added products from biomass has acquired increasing importance due to the high worldwide demand for chemicals and energy, uncertain petroleum availability and the necessity of finding environmentally friendly processes. This paper reports work on the synthesis of several catalysts for the conversion of glucose to methyl lactate. RESULTS: A MCM-41 type mesoporous material containing tin (Si/Sn = 55) was developed with a uniform ordered mesoporous structure, high specific surface area and high pore volume. Sn-MCM-41 was tested in three consecutive catalytic cycles to evaluate its reusability giving methyl lactate yields of 43%, 41% and 39%, in each cycle. The slightly reduction in activity could be explained by the reduction in the accessibility of active centers due to the adsorption of reaction products and structural changes. Microporous titanosilicates and MFI-type zeolite ZSM-5 showed a lower catalytic performance, but exfoliated materials gave higher yields of methyl lactate and pyruvaldehyde dimethyl acetal than their respective layered precursors. CONCLUSIONS: Sn-MCM-41 material showed good results in the conversion of glucose to methyl lactate over three catalytic cycles and exfoliated materials facilitated the access of glucose to the catalytic sites and fast desorption of products.The authors gratefully thank the Spanish Ministry of Economy and Competitiveness (MINECO) for financial support through project MAT2010-15870, as well as the Regional Government of Aragón (DGA), the Obra Social La Caixa (GA-LC-019/2011) and the European Social Fund (ESF). C. Casado also thanks MINECO for the ‘Ramón y Cajal’ program (RYC-2011-08550)

Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts

In this study, we demonstrate how materials science can be combined with the established methods of organic chemistry to find mechanistic bottlenecks and redesign heterogeneous catalysts for improved performance. By using solid-state NMR, infrared spectroscopy, surface and kinetic analysis, we prove the existence of a substrate inhibition in the aldol condensation catalyzed by heterogeneous amines. We show that modifying the structure of the supported amines according to the proposed mechanism dramatically enhances the activity of the heterogeneous catalyst. We also provide evidence that the reaction benefits significantly from the surface chemistry of the silica support, which plays the role of a co-catalyst, giving activities up to two orders of magnitude larger than those of homogeneous amines. This study confirms that the optimization of a heterogeneous catalyst depends as much on obtaining organic mechanistic information as it does on controlling the structure of the support