Dehydration and catalytic cracking reactions can be combined to convert glycerol into light olefins using solid acid catalysts. The combination is suitable for a single-step process to convert glycerol into light olefins at high temperatures (26–36% selectivity at 873 K). However, large quantities of carbon oxides are produced (31–39% COx selectivity), and catalyst deactivation also occurs. High light olefin selectivity (62–65%) and a smaller quantity of carbon oxides (11–12% COx selectivity) can be obtained by using a tandem process involving the dehydration of glycerol and subsequent catalytic cracking of the dehydration products (mainly acetol and acrolein). Furthermore, the ratio of propylene to ethylene can be adjusted by changing the dehydration catalysts to favor the production of acetol or acrolein: Acetol forms propylene, and acrolein forms ethylene. To overcome the fast deactivation of acid catalysts in glycerol dehydration, the hydrogenolysis and catalytic cracking reactions can be synchronized to convert glycerol into hydrocarbons using a combination of metal and acid catalysts. The single-step conversion of glycerol over a metal or bifunctional catalyst formed alcohols and paraffin. The highest selectivity for propylene production (approximately 76%) was obtained in a tandem process via the selective hydrogenolysis of glycerol to propanols over Pt/ZSM-5 catalysts followed by the catalytic dehydration/cracking of propanols to propylene over ZSM-5 catalysts at low temperatures (523 K). The selectivity for propylene was improved by increasing the Si/Al ratio of the ZSM-5 catalysts and the reaction time. Under these conditions, economically competitive crude glycerol (mainly mixtures of glycerol and methanol) can be used to synthesize light olefins (approximately 61% selectivity) with a long lifetime (∼500 h) in single-route reactions by increasing the cracking temperature to 773 K, which is suitable for practical methanol to propylene process.Keywords: Glycerol; Hydrogenolysis; Metal catalyst; Propylene; Zeolite

We report here a strategy for the facile synthesis of hierarchical MFI zeolite nanocrystals with controllable inter-crystalline mesopores by a one-step hydrothermal synthesis method using silica gel as the silica source and tetrapropyl ammonium as the microporous template without any other mesoporous templates or zeolite seeds. Powder X-ray diffraction results show the MFI structure with high crystallinity for all as-prepared zeolites. Scanning electron microscope characterization shows that 400–1000 nm zeolite aggregates are composed of the assembly of ~100 nm zeolite nanocrystals. Transmission electron microscopy results indicate the formation of inter-crystalline mesopores in the aggregated nanocrystals among the interspace of zeolite nanocrystals. The high mesopore volume (0.13 cm3 g−1) and external surface area (93 cm2 g−1) of the aggregated MFI zeolites are observed by N2 sorption measurements. The inter-crystalline porosity of MFI zeolites varies with the change in aggregation and the size of zeolite nanocrystals by changing the sodium concentration or the type of sodium salt in aluminate–silicate gels during hydrothermal crystallization. The mesoporous MFI zeolite aggregates exhibit similar light olefin selectivities and remarkably enhanced lifetime in the catalytic cracking of hexane compared to the highly dispersed MFI zeolite nanocrystals.

•A reaction route to describe borohydride hydrolysis over nickel catalysts.•Presence of boron in nickel catalyst change hydrolysis routes.•Nickel catalysts containing boron possess good hydrolysis activity.The initial hydrogen generation turnover rates during the hydrolysis of sodium borohydride over nickel catalysts (crystalline nickel (Ni), crystalline nickel boride (Ni3B), and amorphous nickel–boron (Ni–B) nanoparticles) were measured to investigate the reaction kinetics and mechanisms by varying the reactant concentrations and reaction temperatures. Nickel catalysts with and without boron follow different hydrolysis pathways; hydroxide ions are involved in the activation of reactant molecules over Ni3B and Ni–B catalysts. This study explicitly reports the zero-order and first-order reaction kinetics with respect to the reactant concentration over Ni, Ni3B and Ni–B catalysts. The initial hydrogen generation turnover rates and activation energies determined from the experimental data indicate that the amorphous Ni–B nanoparticles exhibit the highest turnover rate and lowest activation energy for the hydrolysis of borohydride among the investigated catalysts. This study provides a general strategy for the development of borohydride hydrolysis catalysts via the modification of a metal catalyst using boron, which causes the crystalline structure to become amorphous and leads to electron-rich, highly undercoordinated metal atoms at the surface.

Acid hydrolysis and hydrogenation/hydrogenolysis reactions can be combined for catalytic conversion of cellulose into renewable biorefinery feedstocks by using two heterogeneous catalysts: sulfonic acid (–SO3H) functionalized mesoporous silica (MCM-41) and Ru/C. The combination is suitable for a one-pot tandem process to convert cellulose into alkanediols (mainly propylene glycol and ethylene glycol), yet deactivation of the sulfonic acid (–SO3H) functionalized mesoporous silica occurred rapidly after only one reaction cycle because of an irreversible change in the mesoporous structure and loss of acid groups. However, much better selectivity of hexitol or γ-valerolactone (GVL) can be obtained in a sequential tandem process by hydrogenating the hydrolysis products, glucose and levulinic acid (LA). A similar irreversible deactivation of acid catalyst also occurred when it involved the hydrogenolysis of glucose into alkanediols. When the sulfonic acid-functionalized mesoporous silica is filtered, and the hydrolysis products of cellulose are directly used in the hydrogenation reaction without further purification, a better selectivity and stability of hexitol production can be obtained. Under such conditions, the lifetime of the catalyst system can be significantly extended, up to 6 times the original durability of the acid-functionalized silica.