Niobium and Zirconium Phosphates as Green and Water-Tolerant Catalysts for the Acid-Catalyzed Valorization of Bio-Based Chemicals and Real Lignocellulosic Biomasses

Abstract

Commercial niobium and synthesized zirconium phosphates were tested as water-tolerant heterogeneous acid catalysts in the hydrothermal conversion of different bio-based substrates. Different acid-catalyzed reactions were performed using biomass-derived model compounds and more complex real lignocellulosic biomasses as the substrate. The conversion of glucose and cellulose was preliminarily investigated. Then, a wide plethora of raw lignocellulosic biomasses, such as conifer wood sawdust, Jerusalem artichoke, sorghum, miscanthus, foxtail millet, hemp and Arundo donax, were valorized towards the production of water-soluble saccharides, 5-hydroxymethylfurfural (HMF), levulinic acid (LA) and furfural. The different catalytic performances of the two phosphates were explained on the basis of their acid features, total acidity, Brønsted/Lewis acid sites ratio and strength. Moreover, a better insight into their structure–acidity relationship was proposed. The different acid properties of niobium and zirconium phosphates enabled us to tune the reaction towards target products, achieving from glucose maximum HMF and LA yields of 24.4 and 24.0 mol%, respectively. Remarkably, when real Jerusalem artichoke biomass was adopted in the presence of niobium and zirconium phosphate, maximum yields of furanic compounds and cellulose-derived sugars of 12.7 and 50.0 mol%, respectively, were obtained, after only 1 h of reaction. The synthesized hydrolysates, which were found to be rich in C5 and C6 carbohydrates, can be better exploited for the cascade production of more added-value bio-products.

Molecular Ruthenium Cyclopentadienone Bifunctional Catalysts for the Conversion of Sugar Platforms to Hydrogen

“…[6,8,11,12,15,16,17,18,19] The latter is of particular interest as it can be directly obtained from cellulose by hydrolysis. [20,21,22,23] However, its conversion to hydrogen under the APR conditions is hindered by the production of polymerized side products (humins) above 200 °C, which are temperatures usually needed when using metal-based heterogeneous catalysts. [24,25,26] To address this problem, homogeneous catalysis could help the reaction conditions to be milder, whereas different mechanisms could allow better selectivity.…”

“…In this framework different polyols and sugars have been used as feedstock for aqueous phase reforming, such as ethylene glycol, glycerol, xylitol, fructose and glucose [6,8,11,12,15,16,17,18,19] . The latter is of particular interest as it can be directly obtained from cellulose by hydrolysis [20,21,22,23] . However, its conversion to hydrogen under the APR conditions is hindered by the production of polymerized side products (humins) above 200 °C, which are temperatures usually needed when using metal‐based heterogeneous catalysts [24,25,26] .…”