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The aqueous-phase hydrogenolysis of glycerol was studied in Ni/CeO2 catalytic systems prepared by incipient wetness impregnation. The operating conditions were 34 bar, 227 ºC, 5 wt.% of glycerol, and a W/mglycerol = 20 g catalyst min/g glycerol without a hydrogen supply. The effect of the catalyst preparation conditions on the catalytic activity and physicochemical properties of the catalysts was assessed, particularly the calcination temperature of the support, the calcination temperature of the catalyst, and the Ni content. The physicochemical properties of the catalysts were determined by N2 adsorption, H2-TPR, NH3-TPD, and XRD, among other techniques. A relevant increase in acidity was observed when increasing the nickel content up to 20 wt.%. The increase in the calcination temperatures of the supports and catalysts showed a detrimental effect on the specific surface area and acid properties of the catalysts, which were crucial to the selectivity of the reaction. These catalysts notably enhanced the yield of liquid products, achieving global glycerol conversion values ranging from 17.1 to 29.0% and carbon yield to liquids ranging from 12.6 to 24.0%. Acetol and 1,2-propanediol were the most abundant products obtained in the liquid stream. [ABSTRACT FROM AUTHOR]

Renewable hydrogen production by aqueous phase reforming (APR) over Ni/Al-Ca catalysts was studied using pure or refined crude glycerol as feedstock. The APR was carried out in a fixed bed reactor at 238 °C, 37 absolute bar for 3 h, using a solution of 5 wt.% of glycerol, obtaining gas and liquid products. The catalysts were prepared by the co-precipitation method, calcined at different temperatures, and characterized before and after their use by several techniques (XRD, ICP-OES, H2-TPR, NH3-TPD, CO2-TPD, FESEM, and N2-physisorption). Increasing the calcination temperature and adding Ca decreased the surface area from 256 to 188 m2/g, and its value after the APR changed depending on the feedstock used. The properties of the acid and basic sites of the catalysts influenced the H2 yield also depending on the feed used. The Ni crystallite was between 6 and 20 nm. In general, the incorporation of Ca into Ni-based catalysts and the increase of the calcination temperature improved H2 production, obtaining 188 mg H2/mol C fed during the APR of refined crude glycerol over Ni/AlCa-675 catalyst, which was calcined at 675 °C. This is a promising result from the point of view of enhancing the economic viability of biodiesel. [ABSTRACT FROM AUTHOR]

Glycerol conversion processes such as aqueous phase reforming and hydrogenolysis generate value-added compounds highly diluted in water. Because distillation is a high energy demand separation step, adsorption could be an attractive alternative to recover these chemicals. Adsorption isotherms of 1,2-propanediol, acetol, ethylene glycol and glycerol onto activated carbon were determined by batch adsorption experiments. These isotherms were fitted slightly better to the Freundlich equation than to the Langmuir equation. Acetol is the compound with the highest adsorption at concentrations smaller than 1 M. Properties of the adsorbate such as the −OH group number, chain length, molecular size and dipole moment, besides characteristics of the adsorbent such as the surface area, oxygen and ash content, are considered to explain the observed results. Moreover, adsorption experiments were performed with mixtures of compounds and it was determined that the molar amount adsorbed is less than predicted from the adsorption isotherms of the individual compounds treated separately. In addition, the influence of the activated carbon thermal pre-treatment temperature on the adsorption capacity has been studied, the optimum being 800 °C. An analysis of the influence of the activated carbon characteristics showed that the most important parameters are the total pore volume and the ash content. [ABSTRACT FROM AUTHOR]

The present work studied the stability and reusability of Ni/Al-Fe catalyst in the aqueous phase hydrogenolysis of glycerol without external hydrogen addition. The catalyst based on 28 molar % of Ni with 3/1 molar ratio of Al/Fe was prepared through co-precipitation. This catalyst presented the best performance in our last study which compares several Ni/Al-Fe catalysts with different molar ratios of Al/Fe. To see the influence of the pressurized water on the physicochemical characteristics of Ni/Al-Fe catalyst, a test of up to 9 h has been carried out. Fresh and used catalysts were characterized by various techniques: X-ray Diffraction (XRD), N2-physisorption, field emission scanning electron microscopy (FESEM) and STEM. Glycerol conversion and carbon yield to gases and liquids did not vary significantly when compared at 3 h and 9 h. Furthermore, the morphology of the catalyst remains stable after continuous recycling under severe hydrothermal conditions. The nickel rich phase of the catalyst, which was determined by XRD and scanning transmission electron microscopy (STEM) techniques, showed a stable size after 9 h under reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalysts showed higher yields to ketones, mainly acetol, in the gas phase reactions. • 1,2-propanediol proved to be a highly unreactive compound. • Liquid phase reactions reduced carbonaceous deposit formation, enhancing catalyst stability. • The highest yield to ketones was achieved with the CuAl catalyst with glycerol in the gas phase. • CuAl catalyst exhibited the best performance due to more acid sites and the metallic copper phase. Catalysts based on nickel-aluminum and copper–aluminum were synthesized through the coprecipitation method with a Ni or Cu content of 28 mol%, expressed as Ni/(Ni + Al) or Cu/(Cu + Al). The catalysts were calcined at 675 °C and thoroughly analyzed using various characterization techniques (ICP-OES, N 2 adsorption–desorption, NH 3 -TPD, CO 2 -TPD, XRD, H 2 -TPR and elemental analysis). The samples were tested in two different reaction systems, gas phase at atmospheric pressure and liquid phase at 34 absolute bar, to investigate the production of ketones from glycerol and 1,2-propanediol under reaction conditions of 227 °C and a mass of catalyst/reagent mass flow rate ratio (W/m) of 10 g Catalyst ·min/g Reagent. The characterization results revealed catalysts with high specific surface area and nickel and copper metallic particles, exhibiting good catalytic activity towards liquid products. Gas phase reactions favored the generation of acetol and carbon deposits, which were minimal in liquid phase reactions. The active metal played a crucial role, and it was demonstrated that copper, with a higher number of acidic sites, exhibited greater selectivity towards ketones than the nickel catalyst. The best performance was achieved by the CuAl catalyst in the gas phase reaction of glycerol, with a conversion of 67.0 ± 4.0 %, a carbon selectivity to acetol in the liquid products of 61.4 % and a yield to acetol of 119.8 mg Acetol /g Glycerol. [ABSTRACT FROM AUTHOR]