C.L. Padró

Stability and regeneration of supported PtSn catalysts for propane dehydrogenation

This paper reports the catalytic performance for propane dehydrogenation of Pt and PtSn catalysts on inert supports, studied by means of pulse and flow reaction techniques, in order to determine effects of support on catalytic behavior. K addition to Pt/Al 2 O 3 and PtSn/Al 2 O 3 significantly decreases catalyst deactivation, by lowering the amounts of coke deposited on the support and metal, while producing a coke with a lowe,degree of polymerization. Sn addition to Pt/Al 2 O 3 improves the activity and selectivity to propylene and decreases deactivation. The addition of Sn to Pt/ZnAl 2 O 4 not only enhances activity but also improves catalyst stability. The existence of strong interactions between Pt and Sn, with probable alloy formation, is suggested both on an acidic support like Al 2 O 3 , and on a pH-neutral support like ZnAl 2 O 4 . Bimetallic PtSn/ZnAl 2 O 4 catalysts appear to have the highest stability and reversibility after several reaction steps including the corresponding regeneration steps between them.

Structure and reactivity of alkali-doped calcium oxide catalysts for oxidative coupling of methane

Abstract The effects of the promoter content and the partial pressure of methane and oxygen on the C 2+ hydrocarbon formation, carbon oxides formation and methane conversion in the oxidative coupling of methane over alkali-promoted calcium oxide catalysts were studied in a fixed bed catalytic reactor. It was found that both methane conversion and C 2+ hydrocarbon yield increase substantially with alkali doping up to alkali contents around 2% (molar basis), and then levels off or even decreases slightly. At times-on-stream below 20 min both selectivity to carbon oxides (CO X ) and carbon balances were rather low. In agreement with thermogravimetric and photoelectron spectroscopic data, this was interpreted in terms of catalyst carbonation by the carbon dioxide produced in the reaction during the initial stages of the catalytic run.

Surface characterization and catalytic behaviour of Li/MgO in oxidative coupling of methane

Abstract In this paper a study by XRD, XPS and SEM of the Li/MgO catalyst with different Li content is presented. The catalytic behaviour and the surface composition strongly depends on the Li content. Besides, from the experimental results it can be inferred that di-oxygen species (like O 2 = ) would be present in the catalyst surface and a complex equilibrium between these species and O centers could take place.

A combined experimental and computational study of the esterification reaction of glycerol with acetic acid

AbstractThis work describes theoretical and experimental studies on glycerol esterification to obtain acetins focusing on the obtained isomers. The reaction of glycerol with acetic acid was carried out on Amberlyst 36 wet. Density functional theory calculations on the level of M06-2X functional and 6-311+G(d,p) basis set are carried out and the most stable structures of the reactants and products are located by considering a large number of conformers. The thermodynamics is discussed in terms of the calculated reaction Gibbs free energy. The AIM theory was used to characterize reactants and products. The glycerol esterification with acetic acid is found to be thermodynamically favored, with exothermal property. These agree well with experiments and allow us to explain the relative selectivity of products. FigureGlycerol esterification with acetic acid

Surface Praseodymium Species on MgO: Characterization and Activity for Oxidative Coupling of Methane

On pulsing CH 4 over MgO containing various amounts of praseodymium oxide (PrO x ) at 1023 K, the CH 4 conversion decreased with increasing pulse number, and both the initial activity and selectivity to C 2 products (corresponding to the first pulse) decreased with increasing PrO x content. Characterization by XRD, SEM-EDX and XPS showed calcined materials to contain well-dispersed PrO x (x=1.83-2) at low Pr concentrations, but only crystalline PrO 1.83 at high (10 wt%) Pr concentration. A PrO 1.83 phase was present at all Pr concentrations after the He treatment at 1023 K, and PrO 1.83 , PrO 1.75 and PrO 1.5 after reaction.

Synthesis of bioadditives of fuels from biodiesel-derived glycerol by esterification with acetic acid on solid catalysts

ABSTRACT In this paper, glycerol esterification with acetic acid (AA) was studied on several solid acid catalysts: Al2O3, Al-MCM-41, HPA/SiO2, HBEA, Amberlyst 15 and Amberlyst 36 with the aim of determining the reaction conditions and the nature of the surface acid sites required to produce selectively triacetylglycerol (triacetin). The acidity of the catalysts (nature, density and strength of acid sites) was characterized by temperature-programmed desorption of NH3 and FTIR of adsorbed pyridine. Al2O3 (Lewis acidity) did not show any activity in the reaction. In contrast, highest activity and selectivity to the triacetylated product (triacetin) were obtained on catalysts with Brønsted acidity: Amberlyst 15 and Amberlyst 36. The effect of temperature and molar ratio of AA to glycerol was studied, and the results showed that both parameters have a significant impact on the production of the desired product. Glycerol conversion rate and selectivity to triacetin increased when temperature or AA to glycerol molar ratio were increased, reaching a triacetin yield on Amberlyst 36 of 44% at 393 K and AA to glycerol molar ratio of 6. Deactivation and reusability of Amberlyst 36 were evaluated by performing consecutive catalytic tests. The presence of some irreversible deactivation due to sulfur loss was observed. In addition, the feasibility of using crude glycerol from biodiesel production as reactant was also investigated. Conversion of crude pretreated glycerol yielded values of triacetin and diacetin similar to those obtained with the commercial pure glycerol although at a lower rate.