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Montmorillonite (Mnt)-based solid acids have a wide range of applications in catalysis and adsorption of pollutants. For such solid acids, the acidic characteristic often plays a significant role in these applications. The objective of the current study was to examine the effects of H3PO4-activation and supporting WO3 on the textural structure and surface acidic properties of Mnt. The Mnt-based solid acid materials were prepared by H3PO4 treatment and an impregnation method with a solution of ammonium metatungstate (AMT) and were examined as catalysts in the dehydration of glycerol to acrolein. The catalysts were characterized by nitrogen adsorption-desorption, powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy, temperature programmed desorption of NH3 (NH3-TPD), diffuse reflectance Fourier-transform infrared (DR FTIR) spectroscopy of adsorbed pyridine, and thermogravimetric (TG) analyses. The phosphoric acid treatment of Mnt created Brönsted and Lewis acid sites and led to increases in specific surface areas, porosity, and acidity. WO3 species influenced total acidity, acid strength, the numbers of Brönsted and Lewis acid sites, and catalytic performances. A high turnover frequency (TOF) value (31.2 h−1) based on a maximal 60.7% yield of acrolein was reached. The correlation of acrolein yield with acidic properties indicated that the cooperative role of Brönsted and Lewis acid sites was beneficial to the formation of acrolein and a little coke deposition (<3.3 wt.%). This work provides a new idea for the design of solid acid catalysts with cooperative Brönsted and Lewis acidity for the dehydration of glycerol. [ABSTRACT FROM AUTHOR]

The article underlines and discusses the state-of-the-art accomplishments in the catalytic conversion of glycerol (1,2,3-propanetriol) to fuels and value-added chemicals in the past five years (2008–2012). The reactions include steam reforming, aqueous-phase reforming, hydrogenolysis, oxidation, dehydration, esterification, etherification, carboxylation, acetalization, and chlorination. Typical products are hydrogen, propanediols, dihydroxyacetone, glyceric acid, acrolein, glyceride, polyglycerol, glycerol carbonate, acetals, ketals, and epichlorohydrine. Recent studies on the catalysts, reaction conditions, and possible pathways are primarily discussed. They indicate that major breakthroughs are achieved by the use of multifunctional catalysts, process intensification and integrated reactions. Literature survey suggests that future work on the catalytic conversion of glycerol for commercial goals particularly requires new catalysts, innovative reactor engineering, and close multidisciplinary partnership. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gas-phase dehydration of glycerol over acid-activated sepiolite catalysts was studied. • Glycerol conversion of 92.9% and acrolein selectivity of 59.4% were achieved. • Hydrochloric acid activation changed the texture and acidity of sepiolite. • Texture and acidity affected the conversion of glycerol and selectivity of acrolein. • Coke deposit was found to block the sepiolite channels and to cover the acid sites. In the search for novel solid acid catalysts for the gas-phase catalytic dehydration of glycerol to acrolein, sepiolite clay minerals were activated with hydrochloric acid to produce acid-activated sepiolite catalysts. The effects of the activation process on the texture and acidity of acid-activated sepiolite, and their roles in gas-phase catalytic dehydration of glycerol to acrolein, were then investigated. A series of acid-activated sepiolite catalysts were made from purified natural sepiolite treated with hydrochloric acid of different concentrations (0–8 mol/L) at 80 °C, followed by drying at 100 °C. The acid-activated sepiolite catalyst samples were characterized using X-ray diffraction, X-ray fluorescence analysis, scanning electronic microscopy, thermogravimetric analysis, N 2 adsorption-desorption isotherms, NH 3 -temperature-programmed desorption. Fourier transform-infrared spectroscopy and pyridine adsorption followed by in situ infrared spectroscopy. The catalytic performances in gas-phase catalytic dehydration of glycerol to acrolein were studied using a vertical fixed-bed reactor. Typically, a glycerol conversion of 92.9%, an acrolein selectivity of 59.4%, and a yield of acrolein of 55.2% were achieved when the gas-phase catalytic dehydration of glycerol was conducted over HCl (2 mol/L) acid-activated sepiolite catalyst at 320 °C with an aqueous glycerol solution (20 wt.%) at a rate of 0.10 ml/min as the feedstock and air as the carrier gas at a flow rate of 20 ml/min. The activation of the sepiolite with hydrochloric acid followed by drying can eliminate a portion of the zeolitic water in the tunnels, remove part of the magnesium and aluminum cations in the octahedral sheets of sepiolite, unbundle aggregated sepiolite fibers, and partly break the Si-O-Si in the tetrahedral sheets of sepiolite. These factors increased the porosity, the specific surface area and the acidity of the sepiolite. The partial leaching of magnesium and aluminum ions in the octahedral sheet generated octahedral vacancies and created Mg O Al+ sites in the octahedral sheets, thereby increasing the amount of Lewis acid sites. Along with penetration of H+ cations into the interlayered space of the sepiolite by an ion-exchange reaction and physicochemical surface adsorption, some breakage of the Si O Si bonds in the tetrahedral sheets generated more Si O H+, thus increasing the quantity of Brønsted acid sites. Furthermore, the strength of acidity of the hydrochloric acid-activated sepiolite was significantly changed after the acid activation. The medium-strong Brønsted acid sites (Si O H+ and H+ adsorbed on the surface) appeared to be beneficial for the high conversion of glycerol and the selectivity to acrolein. Lewis acid sites could facilitate the formation of acetol. Under the reaction conditions mentioned above, the coking on the hydrochloric acid-activated sepiolite catalysts readily occurred, rapidly leading to the decrease of the yield of acrolein. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal hydrogenolysis of glycerol to 1,2- propanediol occurred over Cu/MgO. • Basic supports favored to form more 1,2-PDO than neutral and acidic supported ones. • Basicity of support affected the reduction and stabilization of Cu particles. • Deactivation of Cu/MgO resulted from Cu leaching and phase change of Cu species. • Solvent affected the catalytic properties and the deactivation of Cu/MgO catalyst The hydrogenolysis of glycerol is considered a sustainable process to produce 1,2-propanediol (1,2-PDO). However, the development of a cost-effective solid catalyst and a cleaner process minus the addition of external hydrogen remains a challenge. In the present work, a series of Cu/oxide (SiO 2 , MgO, Al 2 O 3 , and ZnO) catalysts were prepared and evaluated for the hydrothermal hydrogenolysis of glycerol. The relationships of structure-catalytic properties were probed by thermogravimetric analysis (TG), powder X-ray diffraction (XRD), nitrogen adsorption-desorption, temperature-programmed desorption of carbon dioxide (CO 2 -TPD), transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS). The catalytic activity of Cu/oxide catalysts was in the order of Cu/Al 2 O 3 < Cu/SiO 2 ≈ Cu/ZnO < Cu/MgO. The Cu/MgO catalysts were identified as highly active catalysts for the hydrothermal hydrogenolysis of glycerol under autogenic pressure without the addition of external hydrogen. When 1.0 g Cu/MgO (Cu/MgO = 0.5, molar ratio) catalyst and 50 g 20 wt% aqueous glycerol solution as the feedstock was loaded in a batch autoclave reactor, the conversion of glycerol reached 55% with a selectivity of 68% to 1,2-propanediol at 473 K after 6 h. Cu0 was identified as the active species both for the catalytic in situ aqueous-phase reforming of glycerol and for the hydrothermal hydrogenolysis of glycerol. The support basicity played a role in stabilizing the Cu nanoparticles on the support surface. During the catalytic reaction, part of Cu species leached from the MgO support into solvent and meanwhile part of Cu species on the support surface aggregated. The basicity and acidity of the solvent affected the behavior of the Cu/MgO catalysts. This work shows that hydrothermal hydrogenolysis process of glycerol is a facile process and the cost-effective Cu/MgO is worth further development for future industrial practice. [ABSTRACT FROM AUTHOR]

Abstract: For the development of efficient solid acid catalysts for the catalytic dehydration of glycerol to acrolein, catalysts made from montmorillonitic clay activated by sulfuric acid were investigated. Montmorillonite was activated in diluted sulfuric acid in the concentration range of 5–40wt.%. The effects of sulfuric acid treatment on the structure of the montmorillonite were characterized by X-ray diffraction, measurements of acidity, N2 adsorption–desorption isotherms, and Fourier transform infrared spectroscopy. The catalytic behavior of sulfuric acid-activated montmorillonite catalysts in the gas-phase dehydration of glycerol were investigated under varying conditions, including the reaction temperature, the feed rate, and the concentration of glycerol. After montmorillonitic clay was activated by sulfuric acid, the layered structural features of montmorillonite remained nearly intact. Ca2+-montmorillonite was changed to H+-montmorillonite by ion exchange reaction during activation. The optimal catalytic glycerol dehydration reaction conditions were found to be: temperature at 320°C, liquid hourly space velocity (LHSV)=18.5h−1, concentration of glycerol solution=10wt.%, and the flow rate of N2 carrier gas=10mL/min. A conversion of 54.2% of glycerol and a yield of 44.9wt.% acrolein were achieved over the montmorillonite catalyst activated by an aqueous 10wt.% sulfuric acid solution. The H+ in the interlayer space of acid-activated montmorillonite catalysts played a critical role in the catalytic dehydration of glycerol. The temperature, the LHSV, and the concentration of glycerol affected the performance of the catalysts through their influence on the reaction mechanism, the contact time, and the reaction equilibrium. [Copyright &y& Elsevier]