Influence of the Surface Chemistry of Multiwalled Carbon Nanotubes on the Selective Conversion of Cellulose into Sorbitol

Abstract

Carbon nanotubes (CNT) were submitted to liquid-phase chemical treatments using HNO3 and subsequently to gas-phase thermal treatments to incorporate different sets of oxygenated groups on the surface. The modified CNT were used as supports for 0.4 wt% Ru in the direct conversion of ball-milled cellulose to sorbitol and high conversions were reached after 3 h at 205 degrees C. Ru supported on the original CNT, although less active, was the most selective catalyst for the one-pot process (70% sorbitol selectivity after 2 h). Unlike the one-pot process, the support acidity greatly promoted the rate of cellulose hydrolysis (35% increase after 2 h) and the glucose selectivity (12% increase after 2 h). The rate of glucose hydrogenation was almost not affected by the support modification. However, the catalyst acidity improved the sorbitol selectivity from glucose. The support acidity was a central factor for the one-pot conversion of cellulose, as well as for the individual hydrolysis and hydrogenation steps, and the original CNT supported Ru catalyst was the most efficient and selective catalyst for the direct conversion of cellulose to sorbitol.