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The hydrogenation reaction of guaiacol in the gas phase at 300 °C and atmospheric pressure of hydrogen was investigated over Ni-based catalysts supported on niobium oxide (Nb2O5) and exfoliated potassium hexaniobate (Nb-exf). The catalysts were prepared by two different methods: photodeposition (pd) and incipient wetness impregnation (im) and were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of ammonia (NH3-TPD) analyses. XRD analysis showed that all catalysts exhibited approximately the same crystallite size of the metallic nickel (15 nm). Regarding the catalytic tests, guaiacol was mainly converted to catechol (59.5–80.6%) and phenol (4.4–14.2%) regardless of the catalyst. Small amounts of benzene were only observed over Ni(im)/Nb2O5. The catalytic experiments showed that the main reaction pathway is the conversion of guaiacol through demethylation reaction producing catechol followed by phenol formation via dehydroxylation reaction. Ni(im)/Nb2O5 was tested for catalytic upgrading of pyrolysis vapor of different biomasses (lignin, microalgae, and malt residue), and it was able to reduce the yield of oxygenated products. The catalytic upgrading of pyrolysis vapor of microalgae using a catalyst-to-biomass weight ratio (C:B) of 3:1 showed the highest selectivity of hydrocarbons (57.44%). The catalyst concentration and the biomass used in the test showed a high influence on the product distribution. [ABSTRACT FROM AUTHOR]

Abstract: CeZrO2/Al2O3 supports with different CeZrO2 loadings were used to obtain stable, high-dispersion Pt (1.5%) catalyts. The solids were evaluated in a conventional fixed-bed reactor and the most stable one was used in a membrane reactor. The fresh and used catalysts were characterized through X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. Pulse experiments were designed to evaluate the oxygen storage capacity of the catalysts. The stable formulation containing 20% CeZrO2 on alumina was shown to be a homogeneous solid solution (Ce0.5Zr0.5O2). The less stable sample, containing 40% of CeZrO2 showed a mixture of phases and its oxygen storage capacity was lower than that of the 20%-loaded formulation. The Pt/20%CeZrO2/Al2O3 catalyst was tested in a membrane reactor built using a self-standing Pd/Ag film with infinite H2 selectivity. When a CH4/CO2 equimolar mixture was fed to the reactor at 823K, WHSV=312h−1, a 75% hydrogen recovery was obtained with a methane conversion 60% above the one that could be obtained in a conventional reactor operating at equilibrium conditions. [Copyright &y& Elsevier]

In the last decades, ethylene production from ethanol was not largely investigated mainly because of the viability and low costs of natural gas and naphtha. Nowadays, ethylene production is usually done by cracking of hydrocarbons. However, the manufacture of ethylene from ethanol is getting more attention mostly due to environmental reasons. The objective of this paper is to compare the equilibrium conversions and compositions of reactions systems involved in ethylene production from ethanol through computational simulations. The obtained results can help to find better operational conditions and elucidate preferential reaction routes involved in ethanol dehydration. [ABSTRACT FROM AUTHOR]

In this work the use of the heterogeneous catalysts pure (LO) and sulfated (SLO) lanthanum oxide, pure HZSM-5 and SLO/HZSM-5 (HZSM-5 impregnated with sulfated lanthanum oxide (SO4 2−/La2O3)) was evaluated. The structural characterization of the materials (BET) showed that the sulfation process led to a reduction of the SLO and SLO/HZSM-5 surface area values. FTIR showed bands characteristic of the materials and, FTIR-pyridine indicated the presence of strong Brønsted sites on the sulfated material. In the catalytic tests the temperature was the parameter that most influenced the reactions. The best reaction conditions were: 10% catalyst, 100°C temperature and 1:5 m OA/m meOH for LO, SLO, SLO/HZSM-5 and 10% catalyst, 100°C temperature and 1:20 m OA/m meOH for HZSM-5. Under these conditions the conversions were: 67% and 96%, for LO and SLO, respectively and 80% and 100%, for HZSM-5 and SLO/HZSM-5, respectively. All catalysts deactivated after the first use, but the deactivation of SLO/HZSM-5 was smaller. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we evaluated the effect of ceria–zirconia content on the performance of Pt/x%CeZrO2/Al2O3 (x =0–40wt.%) during partial oxidation of methane. X-ray diffraction results indicated that, for samples containing 10 and 20wt.% of CeZrO2, there was the formation of a homogeneous solid solution between ceria and zirconia. On the other hand, for Pt/30%CeZrO2/Al2O3, there was the formation of a ceria rich phase and a zirconia rich phase whereas a ceria rich phase and an isolated zirconia phase were detected for Pt/40%CeZrO2/Al2O3. Catalytic tests showed that Pt/Al2O3 exhibited a significant deactivation, while Pt/10%CeZrO2/Al2O3 and Pt/20%CeZrO2/Al2O3 practically did not loose their activity after 24h. A deactivation was detected for Pt/30%CeZrO2/Al2O3 and Pt/40%CeZrO2/Al2O3. The higher stability of the Pt/10%CeZrO2/Al2O3 and Pt/20%CeZrO2/Al2O3 catalysts was attributed to the high reducibility and consequently the high oxygen mobility of the homogeneous solid solution formed, which promoted the mechanism of carbon removal from the metallic particle. [Copyright &y& Elsevier]

Abstract: Ni/CeZrO2 catalysts promoted by Ag, Fe, Pt and Pd were investigated for methane autothermal reforming and partial oxidation of methane. The catalysts properties were determined by BET surface area, X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR), temperature-programmed desorption of CO2 (CO2-TPD) and UV–vis diffuse reflectance spectroscopy (DRS). Nickel dispersions were evaluated using a model reaction, the dehydrogenation of cyclohexane. BET surface area results showed that the catalysts prepared by successive impregnation presented lower surface area which favored the smaller nickel dispersion. XRD analysis showed the formation of a ceria–zirconia solid solution. TPR experiments revealed that the addition of Pt and Pd as promoters increased the reducibility of nickel. CO2-TPD results indicated that the AgNiCZ catalysts presented the best redox properties among all catalysts. The autothermal reforming of methane showed that, among different promoters, the sample modified with silver, AgNiCZ, presented higher methane conversion and better stability during the reaction. These results are related to the good reducibility and to the higher redox capacity observed in TPR and CO2-TPD analysis. Samples prepared by successive impregnation technique resulted in a smaller catalytic activity. For partial oxidation of methane, just as happened in autothermal reforming, AgNiCZ also presented the best performance during the 24h of reaction and the addition of silver by successive impregnation resulted in a lower methane conversion, probably, due to the smaller metal dispersion. [Copyright &y& Elsevier]

Abstract: In this work, the effect of the thermal treatment temperature of the support on the behavior of Pt/CeZrO2/Al2O3 catalysts on the methane partial oxidation was evaluated. BET surface area, metal dispersion and oxygen storage capacities and hydrogen consumption during TPR decreased with the increase of the thermal aging temperature. During the reaction of partial oxidation of methane, Pt/CeZrO2/Al2O3 aged at 1073 and 1173K presented the best performance. This result was attributed to the higher reducibility of the support and to the larger metal dispersion presented by these materials. These properties favor the carbon removal mechanism from the metal surface, avoiding deactivation. [Copyright &y& Elsevier]

Abstract: The effect of the preparation method of Pt/CeZrO2/Al2O3 catalysts on the dispersions of the metal and of the ceria–zirconia on the surface of the alumina and on the catalytic performance of methane partial oxidation reaction was evaluated. The ceria–zirconia materials were supported on the alumina surface by precipitation and impregnation and all the samples contained 1.5wt.% of Pt. The dispersion of the ceria–zirconia was evaluated by adsorbed CO2 infrared spectroscopy and the dispersion of the metal was determined by the dehydrogenation of cyclohexane. The reducibility of the catalysts was measured by oxygen storage capacity and temperature programmed reduction. The samples prepared by impregnation present higher activity, stability and selectivity to form CO and H2 than the ones prepared by precipitation. The characterization results show that all the samples had practically the same platinum dispersion but the dispersion of the ceria–zirconia material on the alumina was more effective when the impregnation method was used. The impregnation favors a high coverage degree of the alumina by the ceria-based oxides. This means that a larger fraction of platinum particles is in contact with ceria or ceria–zirconia oxide. The metal–support interface is a key factor to avoid the carbon deposits that are responsible for the deactivation of some samples. [Copyright &y& Elsevier]