Conversion of Biomass into Chemicals over Metal Catalysts

This review surveys recent advances in the applications of layered double hydroxides (LDHs) in heterogeneous catalysis. By virtue of the flexible tunability and uniform distribution of metal cations in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment and/or reduction-have found many applications as stable and recyclable heterogeneous catalysts or catalyst supports for a variety of reactions with high industrial and academic importance. A major challenge in this rapidly growing field is to simultaneously improve the activity, selectivity and stability of these LDH-based materials by developing ways of tailoring the electronic structure of the catalysts and supports. Therefore, this Review article is mainly focused on the most recent developments in smart design strategies for LDH materials and the potential catalytic applications of the resulting materials.

Catalytic applications of layered double hydroxides: recent advances and perspectives

Research interest in biomass conversion to fuels and chemicals has increased significantly in the last decade as the necessity for a renewable source of carbon has become more evident. Accordingly, many different reactions and processes to convert biomass into high-value products and fuels have been proposed in the literature. Special attention has been given to the conversion of lignocellulosic biomass, which does not compete with food sources and is widely available as a low cost feedstock. In this review, we start with a brief introduction on lignocellulose and the different chemical structures of its components: cellulose, hemicellulose, and lignin. These three components allow for the production of different chemicals after fractionation. After a brief overview of the main reactions involved in biomass conversion, we focus on those where bimetallic catalysts are playing an important role. Although the reactions are similar for cellulose and hemicellulose, which contain C6 and C5 sugars, respectively, different products are obtained, and therefore, they have been reviewed separately. The third major fraction of lignocellulose that we address is lignin, which has significant challenges to overcome, as its structure makes catalytic processing more challenging. Bimetallic catalysts offer the possibility of enabling lignocellulosic processing to become a larger part of the biofuels and renewable chemical industry. This review summarizes recent results published in the literature for biomass upgrading reactions using bimetallic catalysts.

Bimetallic catalysts for upgrading of biomass to fuels and chemicals

This Critical Review provides an overview of the recent developments in the synthesis and characterization of bimetallic nanoparticles. Initially the review follows a materials science perspective on preparing bimetallic nanoparticles with designer morphologies, after which the emphasis shifts towards recent developments in using these bimetallic particles for catalysing either oxidation or reduction. In the final part of this review we present an overview of the utilization of bimetallic catalyst systems for the transformation of bio-renewable substrates and reactions related to the realization of a bio-refinery. Because of the sheer number of examples of transformations in this area, a few key examples, namely selective oxidation, hydrogenation/hydrogenolysis and reforming of biomass derived molecules, have been chosen for this review. Reports of bimetallic catalysts being used for the aforementioned transformations are critically analysed and the potential for exploiting such bimetallic catalysts have also been highlighted. A specific objective of this review article is to motivate researchers to synthesize some of the “designer” bimetallic catalysts with specific nanostructures, inspired from recent advances in the area of materials chemistry, and to utilize them for the transformation of biomass derived materials that are very complex and pose different challenges compared to those of simple organic molecules. We consider that supported bimetallic nanoparticles have an important role to play as catalysts in our quest for a more green and sustainable society.

Designing bimetallic catalysts for a green and sustainable future

Graphene oxide: A promising nanomaterial for energy and environmental applications

Homogenously dispersed copper on layered solid base (Cu0.4/Mg5.6Al2O8.6-CP, with 80.1% dispersion of copper) was synthesized via thermal decomposition of the as-synthesized Cu0.4Mg5.6Al2(OH)16CO3 layered double hydroxides. This bi-functional highly dispersed Cu-solid base catalyst is extremely effective for hydrogenolysis of aqueous glycerol. The detected conversion of glycerol reached 80.0% with a 98.2% selectivity of 1,2-propanediol at 180 °C, 3.0 MPa H2 and 20 h. But copper dispersed poorly in those catalysts prepared via impregnation and ion-exchange, and their activities were lower. These precursors and catalysts were characterized by N2-adsorption, X-ray diffraction, scanning electronic microscope, transmission electronic microscope, thermo-gravimetry, temperature-programmed reduction with H2, in-situ XRD, dissociative N2O adsorption and CO2 temperature-programmed desorption. It was confirmed that the as-synthesized Cu0.4Mg5.6Al2(OH)16CO3 showed a well crystallized layer-structure of hydrotalcite and copper dispersed homogenously on the layer-structure of hydrotalcite after thermal decomposition and H2 reduction.

Hydrogenolysis of glycerol over homogenously dispersed copper on solid base catalysts

Hydrogenolysis of glycerol over Cu0.4/Zn5.6−xMgxAl2O8.6 catalysts: The role of basicity and hydrogen spillover

A series of bimetallic Pd-Cu/solid-base catalysts were prepared via thermal decomposition of Pd x Cu 0.4 Mg 5.6− x Al 2 (OH) 16 CO 3 layered double hydroxides precursors and used in hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). X-ray diffraction (XRD), scanning electron microscopy (SEM) and N 2 O oxidation and followed H 2 titration characterizations confirmed that well structured layered double hydroxides Pd x Cu 0.4 Mg 5.6− x Al 2 (OH) 16 CO 3 crystals could be prepared when the amount of added Pd was less than x x Cu 0.4 /Mg 5.6− x Al 2 O 8.6− x and Pd improved the reduction of Cu. Hydrogenolysis of glycerol proceeded easily on bimetallic Pd-Cu/solid-base catalysts than separated Pd and Cu. On Pd 0.04 Cu 0.4 /Mg 5.56 Al 2 O 8.56 , the conversion of glycerol and selectivity of 1,2-PDO reached 88.0 and 99.6%, respectively, at 2.0 MPa H 2 , 180 °C, 10 h in ethanol solution. And this catalyst is stable in five recycles. It was concluded that H 2 -spillover from Pd to Cu increased the activity of Pd x Cu 0.4 /Mg 5.6− x Al 2 O 8.6− x in hydrogenolysis of glycerol.

Hydrogenolysis of glycerol on bimetallic Pd-Cu/solid-base catalysts prepared via layered double hydroxides precursors

Rod-like MnO2 uniformly attached on both side of GO sheets (MnO2/GO) is an efficient heterogeneous catalyst for the synthesis of primary amides from primary alcohols and ammonia as well as from aldehydes or nitriles. Water is the best solvent for these reactions, analytically pure crystals of product could be isolated by simply cooling in ice and this catalyst has excellent recyclability.

Shuixin Xia

Papers

Hydrogenolysis of glycerol over homogenously dispersed copper on solid base catalysts

Hydrogenolysis of glycerol over Cu0.4/Zn5.6−xMgxAl2O8.6 catalysts: The role of basicity and hydrogen spillover

Hydrogenolysis of glycerol on bimetallic Pd-Cu/solid-base catalysts prepared via layered double hydroxides precursors

MnO2/graphene oxide: a highly active catalyst for amide synthesis from alcohols and ammonia in aqueous media

Transesterification of Glycerol with Dimethyl Carbonate to Glycerol Carbonate over Na-Based Zeolites