C. García-Sancho

Dehydration of Xylose to Furfural over MCM-41-Supported Niobium-Oxide Catalysts

A series of silica-based MCM-41-supported niobium-oxide catalysts are prepared, characterized by using XRD, N2 adsorption-desorption, X-ray photoelectron spectroscopy, Raman spectroscopy, and pyridine adsorption coupled to FTIR spectroscopy, and tested for the dehydration of D-xylose to furfural. Under the operating conditions used all materials are active in the dehydration of xylose to furfural (excluding the MCM-41 silica support). The xylose conversion increases with increasing Nb2 O5 content. At a loading of 16 wt % Nb2 O5 , 74.5 % conversion and a furfural yield of 36.5 % is achieved at 170 °C, after 180 min reaction time. Moreover, xylose conversion and furfural yield increase with the reaction time and temperature, attaining 82.8 and 46.2 %, respectively, at 190 °C and after 100 min reaction time. Notably, the presence of NaCl in the reaction medium further increases the furfural yield (59.9 % at 170 °C after 180 min reaction time). Moreover, catalyst reutilization is demonstrated by performing at least three runs with no loss of catalytic activity and without the requirement for an intermediate regeneration step. No significant niobium leaching is observed, and a relationship between the structure of the catalyst and the activity is proposed.

Dehydration of xylose to furfural using a Lewis or Brönsted acid catalyst and N2 stripping

Abstract The activity of Lewis (Nb2O5) and Bronsted (Amberlyst 70) acid catalysts for the cyclodehydration of xylose to furfural was studied. The nature of the acidity resulted in significant changes in the reaction mechanism. Lewis acid sites promote the formation of xylulose, while Bronsted acid sites are required to further dehydrate the sugar to furfural. Amberlyst 70 in water/toluene at 175 °C showed lower activity but gave a higher furfural yield. Using N2 as the stripping agent considerably improved the furfural yield and product purity in the stripped stream. Catalyst stability was also studied.

Porous Silicon-Based Catalysts for the Dehydration of Glycerol to High Value-Added Products

Increasing worldwide biodiesel production has led to the generation of an important glycerol surplus, which needs to be valorized in order to improve the economic and environmental sustainability of the biodiesel industry. In this context, glycerol dehydration to acrolein by acid catalysis appears to be a potential route of glycerol valorization, since acrolein is an important intermediate for many chemical industries. The main drawback of this catalytic process is catalyst deactivation. Different alternatives have been proposed for overcoming it, such as the use of mesoporous materials in order to facilitate the diffusion of glycerol and reaction products, thus minimizing deactivation. This review compiles the main achievements of the use of mesoporous silica-containing materials that have been deployed either as a catalyst or for support in glycerol dehydration to acrolein. Thus, the effect of mesoporosity on both catalytic performance and deactivation will be discussed, as well as the blocking of pores by coke deposition.