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Zinc aluminate (ZnAl) was used as support to obtain a series of rhodium-modified Co-ZnAl catalysts for the catalytic oxidation of propane and naphthalene. The catalysts were characterized by various techniques including N2 adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), diffuse reflectance spectroscopy (DRS), FTIR and X-ray photoelectron spectroscopy (XPS), to correlate chemical and physical characteristics with catalytic properties. TPR and XPS techniques show the presence of segregated cobalt compounds, as well as cobalt species interacting with the support. Segregated cobalt species are considered responsible for the catalytic activity, due to their high reducibility. The addition of Rh promotes the reducibility of the cobalt compounds yielding to an increase in the surface content of Co2+. For propane oxidation, the best activity shown by the Rh(0.5)Co(5)-ZnAl sample could be associated with a synergic effect between rhodium and cobalt species. No specific effects were revealed due to the addition rhodium for the naphthalene oxidation.

In this work, zinc aluminate spinel powders were prepared by a fast, simple, eco-friendly and low-cost modified Pechini method using commercial gelatin as the organic precursor. The materials were calcinated at 600, 700 and 800 °C and characterized by thermogravimetric analysis, in situ and ex situ X-ray diffraction (XRD), N2-adsorption/desorption isotherms and scanning electron microscopy. The results showed that single phase ZnAl2O4 particles with spinel structure were successfully obtained resulting in a high purity, nanometric, homogeneous and mesoporous materials. The in situ XRD results showed that the crystalline spinel structure of ZnAl2O4 started forming at a temperature lower than 600 °C, revealing powders with crystallite size smaller than 40 nm, which increased with increasing the temperature (91% of increase between 600 and 800 °C). The effect of calcination time showed that the materials calcinated at 600 °C for 3 h presented the higher percentage of crystallite growth due to the increase of crystallinity. The ZnAl2O4 samples retained their pore size up to 700 °C. Resumo Neste trabalho, pós do espinélio aluminato de zinco foram preparados por um método Pechini modificado, rápido, simples, ambientamento seguro e de baixo custo, utilizando gelatina comercial como precursor orgânico. Os materiais foram calcinados a 600, 700 e 800 °C e caracterizados por análise termogravimétrica, difratometria de raios X (DRX) in situ e ex situ, isotermas de adsorção/dessorção de N2 e microscopia eletrônica de varredura. Os resultados mostraram que as partículas de ZnAl2O4 monofásicas com estrutura espinélio foram obtidas com sucesso resultando em materiais de alta pureza, nanométricos, homogêneos e mesoporosos. Os resultados de DRX in situ mostraram que a estrutura cristalina do espinélio ZnAl2O4 começou a se formar em temperaturas inferiores a 600 °C, revelando pós com tamanho de cristalito menor que 40 nm, que cresceram com o aumento da temperatura (91% de aumento entre 600 e 800 °C). O efeito do tempo de calcinação mostrou que os materiais calcinados a 600 °C por 3 h apresentaram maior porcentagem do crescimento do cristalito devido ao aumento da cristalinidade. As amostras de ZnAl2O4 mantiveram o tamanho dos poros até 700 °C.

Palladium-modified Co-ZnAland Cu-ZnAl materials were used and found active for the catalytic oxidation of propene and propane. According to the results obtained by XRD, TPR and XPS, the zinc aluminate-supported phases are oxide phases, Co3O4, CuO and PdOx for Co-ZnAl, Cu-ZnAl and Pd-ZnAl catalysts, respectively. These reducible oxide species present good catalytic activity for the oxidation reactions. The addition of palladium to Co-ZnAl or Cu-ZnAl samples promoted the reducibility of the system and, consequently, produced a synergic effect which enhanced the activity for the propene oxidation. The PdCo-ZnAl sample was the most active and exhibited highly dispersed PdOx particles and surface structural defects. In addition, it exhibited good catalytic stability. The H2 pre-treated PdCu-ZnAl, PdCo-ZnAl and Pd-ZnAl samples showed higher activity than the original oxide catalysts, evidencing the important role of the oxidation state of the species, mainly of the palladium species, on the catalytic activity for the propene combustion. The synergic effect between metal transition oxides and PdOx could not be observed for the propane oxidation.

Zinc aluminate (ZnAl2O4) particles with a spinel structure were prepared by metal-chitosan complexation method. The solids were obtained by the thermal decomposition of precursor compound of metallic hydroxides mixture and the biopolymer chitosan. X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and N2-adsorption–desorption isotherms were used for the characterization of the products. The results showed that the ZnAl2O4 spinel can be obtained by heating the precursor at temperatures above of 500 °C, resulting in a material with porous structure and large surface area and high purity.

The catalytic performance of Pt, PtSn and PtGe supported on ZnAl2O4 obtained by mechanochemical synthesis (MS) or coprecipitation (COPR) is studied in the production of 1-decene from the n-decane dehydrogenation. The effect of preparation methods and Sn and Ge addition to Pt on the activity and selectivity was analyzed. The catalytic characterization was carried out by using XRD, Specific surface area, 2-propanol dehydration reaction, equilibrium pH, cyclohexane dehydrogenation (CHD), cyclopentane hydrogenolysis (CPH), TPR, H2 chemisorption, XPS, TPO, and TEM. Characterization studies indicate that the addition of Sn to the Pt metal phase modifies not only the catalytic properties, but deactivation and stability as well. PtSn catalysts on both spinels were more active, with lower activity fall than PtGe ones and the higher the Sn loading, the more noticeable this effect. Besides, PtSn catalysts supported on ZnAl2O4 MS showed a more stabilizing effect. Fil: Ballarini, Adriana Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: de Miguel, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Castro, Alberto Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Scelza, Osvaldo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

The effect of preparation method (sol-gel, wet mixing or coprecipitation) on the surface structure of zinc aluminate is reported. Coprecipitated and sol-gel prepared ZnAl2O4 were found to be present spinel structure. If calcium was added during synthesis, it was found to be deposited on top of the spinel surface while, if tin was added, the surface of ZnAl2O4 was reconstructed. These aluminates were impregnated with platinum and tested in the isobutane dehydrogenation. The characterization techniques used were LEIS and X-ray diffraction.