J. Santamaría-González

Catalytic behavior of vanadium-containing mesoporous silicas in the oxidative dehydrogenation of propane

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established.

Dehydration of Xylose to Furfural over MCM-41-Supported Niobium-Oxide Catalysts

A series of silica-based MCM-41-supported niobium-oxide catalysts are prepared, characterized by using XRD, N2 adsorption-desorption, X-ray photoelectron spectroscopy, Raman spectroscopy, and pyridine adsorption coupled to FTIR spectroscopy, and tested for the dehydration of D-xylose to furfural. Under the operating conditions used all materials are active in the dehydration of xylose to furfural (excluding the MCM-41 silica support). The xylose conversion increases with increasing Nb2 O5 content. At a loading of 16 wt % Nb2 O5 , 74.5 % conversion and a furfural yield of 36.5 % is achieved at 170 °C, after 180 min reaction time. Moreover, xylose conversion and furfural yield increase with the reaction time and temperature, attaining 82.8 and 46.2 %, respectively, at 190 °C and after 100 min reaction time. Notably, the presence of NaCl in the reaction medium further increases the furfural yield (59.9 % at 170 °C after 180 min reaction time). Moreover, catalyst reutilization is demonstrated by performing at least three runs with no loss of catalytic activity and without the requirement for an intermediate regeneration step. No significant niobium leaching is observed, and a relationship between the structure of the catalyst and the activity is proposed.

Catalytic behaviour of chromium supported mesoporous MCM-41 silica in the oxidative dehydrogenation of propane

A series of chromium supported mesoporous MCM‐41 silica catalysts (0.5–6 wt% Cr) were prepared and tested in the oxidative dehydrogenation of propane between 350 and 550°C. The catalytic activity, observed at temperatures as low as 350 °C, can be well explained on the basis of the existence of highly dispersed and reducible chromium species.

Cobalt supported on zirconium doped mesoporous silica: a selective catalyst for reduction of NO with ammonia at low temperatures

A zirconium doped mesoporous silica has been used as a support of cobalt oxide (4–16 wt.% Co), and tested in the selective catalytic reduction (SCR) of NO with ammonia in an excess of oxygen. These catalysts exhibit maximum conversion of NO (88%) at low temperature (200 ◦ C), with an almost stoichiometric conversion of NH3 and minimal N2O formation. Moreover, the catalytic activity can be correlated to the presence of well dispersed Co 2+ /Co 3+ species, as evidenced by different characterisation techniques, and their capacity to adsorb NO molecules.

Selective Catalytic Reduction of NO by Ammonia at Low Temperatures on Catalysts Based on Copper Oxide Supported on a Zirconium-Doped Mesoporous Silica

Copper-oxide-containing zirconium-doped mesoporous silica catalysts (1–12 wt% Cu) have been tested in the selective catalytic reduction of NO by ammonia in excess of oxygen. The catalyst with 6 wt% Cu exhibits a maximum NO conversion of 94% at low temperature (250 °C), with a stoichiometric conversion of ammonia and minimal N2O formation. The catalytic behavior can be correlated with the high degree of dispersion and easy reduction of the supported CuO.

Silica pillared metal(IV) phosphate materials as supports for nickel catalysts

Two silica pillared phosphate materials containing different amounts of silica have been used as supports to prepare, by impregnation, two series of metallic nickel catalysts (8, 10 and 15% loading). Thermal programmed reduction curves of nickel show two peaks at ca. 690 and 838 K denoting two different sites for Ni 2+ ions assigned to the external and inner surface, respectively. These high reduction temperatures indicate high dispersion and strong interactions with the supports. XPS analyses show that the reduction degree at 873 K (2 h) ranges between 22.5 and 30%. The metal dispersion and particle size were calculated from hydrogen adsorption isotherms at 298 K. These nickel catalysts are active in the hydrogenation of benzene (at 443 K). In both series of catalysts no correlation between activities and metal dispersion was found, and turnover frequencies indicate an apparent structure sensitivity of the reaction, likely to be due to the presence of superficial unreduced nickel ions. TEM micrographs reveal that deactivation of catalyst occurs by formation of coke and filaments of carbon separating the nickel particles from the pillared materials.

Copper supported on mixed alumina/gallium oxide pillared α-tin phosphate for De-NOx applications

Alumina- and mixed alumina/gallium oxide-pillared α-tin phosphate have been impregnated with different amounts of copper via the incipient wetness method. Their characterization by X-ray photoelectron spectroscopy, H2 temperature-programmed reduction and NO temperature-programmed desorption has allowed to gain insight into the nature of the copper species. These are present as small CuO clusters (not detectable by XRD) as well as forming part of spinel-like structures. NO-TPD studies show that only NO is desorbed from all the catalysts. Ga3Al11-SnP with 4.9 wt% Cu interacts most strongly with NO and this catalyst exhibits the highest degree of reduction of Cu2+ to Cu+ after the catalytic reaction. The catalysts are active for the selective catalytic reduction (SCR) of nitric oxide with propane in the presence of excess oxygen.

Porous silica pillared α-ZrTi phosphate-phosphonates materials

Abstract By the sol-gel method, there have been prepared different phosphate-phosphonates of zirconium-titanium with formula Zr 0.75 Ti 0.25 (HPO 4 ) 2− x (C 6 H 5 PO 3 ) x , X varies from 0.65 to 1.8. The intercalation of hydrolysed derivatives from aminopropyl-triethoxysilane, NH 2 (CH 2 ) 3 Si(OC 2 H 5 ) 3 , into these compounds gives rise, after heating at 773 K, to the formation of silic pillars between the layers, with basal spacing approximately 14.5 A, surface area up to 149m 2 /g and high acidity (1.1-1.6 mmol NH 3 g −1 between 373–673 K).

Chromium-impregnated mesoporous silica as catalysts for the oxidative dehydrogenation of propane

The activity of chromium-supported silica catalysts in the oxidative dehydrogenation of propane at 300–550°C has been investigated varying the Cr content between 0.5 and 6.0 wt%. XPS and diffuse reflectance spectroscopy indicate the existence in all materials of Cr species with two different oxidation states: Cr(III) and Cr(VI). After impregnation, textural parameters of the mesoporous MCM-41 silica are barely affected. These catalysts are active in the oxidative dehydrogenation of propane at temperatures as low as 300°C. Activity and selectivity are correlated to the presence of highly dispersed Cr(III) species and increase with the reaction temperature. Thus, the catalyst which presents the highest loading of Cr, without evidence of the presence of crystallites of Cr 2 O 3 (1.5Cr-MCM), is the most active for this catalytic reaction.

Aluminum doped mesoporous silica SBA-15 for glycerol dehydration to value-added chemicals

A series of Al-grafted mesoporous SBA-15 silica was synthesized and tested as catalysts in the gas-phase dehydration of glycerol to acrolein. Different Si/Al molar ratios were employed to tune the structure, texture and acidity of catalysts in order to analyze their effect on the catalytic performance. Different characterization techniques, such as powder X-ray diffraction, X-ray photoelectron spectroscopy, 27Al MAS NMR, N2 adsorption–desorption at −196 °C, ammonia temperature programmed desorption (NH3-TPD) and adsorption of pyridine coupled to Fourier transform infrared spectroscopy were employed. All materials were active in glycerol dehydration, being acrolein the main product in all cases. The catalyst with the highest Al content (AlSBA-2.5) showed the highest acrolein yield (27.6%) after 8 h of time-on-stream. A clear relationship between the effective production of acrolein and the acidity of catalysts could be established. Catalysts suffered from deactivation by coke deposition on the surface, but they can be reused, at least during three catalytic cycles, after regeneration at 550 °C in air during 4 h after each cycle.Graphical Abstract