Influence of the Incorporation of Basic or Amphoteric Oxides on the Performance of Cu-Based Catalysts Supported on Sepiolite in Furfural Hydrogenation

Abstract

Cu-based catalysts supported on sepiolite have been tested in vapor-phase hydrogenation of furfural. The incorporation of basic or amphoteric metal oxides (magnesium oxide, zinc oxide, or cerium oxide) improves the catalytic behavior, reaching a maximum furfural conversion above 80% after 5 h of reaction at 210 °C. In all cases, the main product is furfuryl alcohol, obtaining 2-methylfuran in lower proportions. The incorporation of these metal oxide species ameliorates the dispersion of metallic Cu nanoparticles, increasing the number of available Cu0-sites, which enhances the catalytic performance. The presence of acid sites favors the hydrogenolysis of furfuryl alcohol towards 2-methylfuran, although it also causes an increase of carbon species on its surface, which is associated with the catalytic deactivation of the catalyst along the time-on-stream.

Gas-Phase Hydrogenation of Furfural to Furfuryl Alcohol over Cu-ZnO-Al2O3 Catalysts Prepared from Layered Double Hydroxides

“…In this sense, the formation of MF is favored by the existence of weak acid sites associated to the aluminosilicate, used as support, (kerolite) and the presence of a small fraction of Cu + species. In these studies, the incorporation of promoters, such as ZnO, MgO or CeO 2 , modified the selectivity pattern, with an increase in the FOL yield due to milder interaction between support and Cu species, as indicated their H 2 -TPR data [29,37,70], which is in agreement with data reported in the present work.…”

“…The worsening of the conversion at higher reaction temperature was attributed to FUR polymerization, due to its strong adsorption on the active sites involved in the hydrogenation process. This trend was not observed in the present work, which could be explained by the meso-and macroporosity of catalysts and the relatively low concentration of acid sites, in such a way that the FUR-active site interaction is weaker, so the desorption of FUR and reaction products should be easier [29,37,70]. With regard to the hydrogenation products ( Figures 11B,C), in all cases, the main product was FOL, reaching a maximum yield of 65% after 5 h of TOS at 210 °C.…”

“…However, the hydrogenation FUR → FOL takes place on the metallic sites [28,29] and it does not seem to be affected by the textural properties of catalysts. This fact was confirmed in Cu-based catalysts supported on clay minerals [33,37,70]. Thus, those catalysts with very poor textural properties, like bentonite, or whose pore dimensions hinder the incorporation of Cu nanoparticles, like sepiolite, only dispersed metal nanoparticles on the catalyst surface [33].…”

“…However, the presence of weak acid sites could exert a beneficial effect on the catalytic behavior, since the interaction between FUR, or reaction products, and the catalyst is weakened in comparison with catalyst with higher acidity, thus favoring the desorption of products adsorbed on the catalyst surface. In this sense, several supports, such as SiO 2 or clay minerals, with similar amount of acid sites [29,37], have provided good catalytic activity in FUR hydrogenation, under similar experimental conditions.…”

“…The presence of these acid sites is ascribed to Al 2 O 3 and Cu + , which provide Lewis acid sites, and even to ZnO due to its amphoteric character, similar to alumina. Several authors have reported that the modulation of the acidity plays a key role in FUR conversion, since a high number of acid sites can cause the polymerization of FUR, mainly in gas-phase, leading to the formation of a high proportion of carbonaceous deposits [29,37,62]. These polymerized FUR species interact strongly with the active sites, in such a way that catalysts tend to be deactivated relatively fast.…”