José Mansur Assaf

Influence of calcium content in Ni/CaO/γ-Al2O3 catalysts for CO2-reforming of methane

Abstract In order to improve the thermal stability and carbon-deposition resistance of the Ni/γ-Al2O3 during the reforming of methane with carbon dioxide, the catalyst was modified by adding an alkaline earth (CaO). The catalysts were prepared by successive impregnation of Ni and Ca on alumina, varying the impregnation order. It was found that calcium decreases the sintering resistance of the support and blocks the small pores, especially when it is added above the nickel. It has also been reported that calcium competes with nickel in the interaction with the support, favoring the formation of nickel species being more easily reducible, when it is added first. In catalytic tests, it has been showed that, in low quantities, calcium increases the catalytic conversion, probably due to attraction effects between CaO and CO2, while in high quantities, calcium decreases the catalytic activity, this effect being associated with the increase in electron density of the catalyst.

Ni/Al2O3 catalysts: effects of the promoters Ce, La and Zr on the methane steam and oxidative reforming reactions

The influence of the promoters CeO2, CeO2–ZrO2 and CeO2–La2O3 on the reactivity of γ-Al2O3 supported nickel catalysts from steam and oxidative reforming of methane was investigated in this study. At temperatures above 500 °C, promoted catalysts showed the best performance in the methane oxidative reforming reaction. The increase in activity can be attributed to the specific catalyst–promoter interactions such as the capacity of CeO2 to store and release oxygen and the influence of La2O3 on the stability of the support. Below 500 °C, the activity of the catalyst may be related more directly to the exposed metal surface area.

Synthesis and Characterization of LaNiO3, LaNi(1-x)Fe xO3 andLaNi(1-x)Co xO3 Perovskite Oxides for Catalysis Application

Mixed metal oxides with perovskite-type structure show a great potential to be used in catalysis, electrocatalysis and electronic ceramics. Perovskites oxides catalysts with the composition LaNiO3, LaNi(1-x)FexO3 and LaNi(1-x)CoxO3 (x = 0.4 and 0.7) have been synthesized by the precipitation method to be used in the methane reforming to produce hydrogen and synthesis gas. The compounds were characterized by X-ray diffraction, thermogravimetric and differential thermal analysis, inductively coupled plasma atomic emission spectroscopy, surface area measurements, energy dispersive X-ray spectrometry coupled to scanning electron microscopy and temperature programmed reduction. The results showed that a suitable combination of the preparation method with calcination variables (time and temperature) could result in oxides with the desired structure and with important properties at the application point of view in heterogeneous catalysis.

Produção de hidrogênio a partir da reforma a vapor de etanol utilizando catalisadores Cu/Ni/gama-Al2o3

Cu/Ni/g-Al2O3 catalysts were prepared by an impregnation method with 2.5 or 5% wt of copper and 5 or 15% wt of nickel and applied in ethanol steam reforming. The catalysts were characterized by atomic absorption spectrophotometry, X-ray diffraction, temperature programmed reduction with hydrogen and nitrogen adsorption. The samples showed low crystallinity, with the presence of CuO and NiO, both as crystallites and in dispersed phase, as well as of NiO-Al2O3. The catalytic tests carried out at 400 oC, with a 3:1 water/ethanol molar ratio, indicated the 5Cu/5Ni/Al2O3 catalyst as the most active for hydrogen production, with a hydrogen yield of 77% and ethanol conversion of 98%.

MATHEMATICAL MODELLING OF METHANE STEAM REFORMING IN A MEMBRANE REACTOR: AN ISOTHERMIC MODEL

A mathematical modelling of one-dimensional, stationary and isothermic membrane reactor for methane steam reforming was developed to compare the maximum yield for methane conversion in this reactor with that in a conventional fixed-bed reactor. Ficks first law was used to describe the mechanism of hydrogen permeation. The variables studied include: reaction temperature, hydrogen feed flow rate and membrane thickness. The results show that the membrane reactor presents a higher methane conversion yield than the conventional fixed-bed reactor.

Hollow AgPt/SiO2 nanomaterials with controlled surface morphologies: is the number of Pt surface atoms imperative to optimize catalytic performances?

We describe herein an investigation on how the number of Pt surface atoms and nature of exposed surface facets affect the catalytic performances of AgPt nanomaterials displaying controlled surface morphologies (smooth or rough surfaces), shapes (spherical or one-dimensional), and hollow interiors towards CO oxidation. More specifically, we focused on AgPt nanoshells (smooth surfaces), assembled nanoparticles (rough surfaces), nanotubes with smooth surfaces, and nanotubes with rough surfaces. We found that their catalytic performances followed the order: nanotubes with smooth surfaces > nanoshells, nanotubes with rough surfaces > assembled nanoparticles. The better catalytic activity observed for the nanoshells relative to the assembled nanoparticles can be associated with their higher number of Pt surface atoms. Even though the nanotubes with rough surfaces had a higher number of Pt surface atoms relative to the nanotubes with smooth surfaces, the latter displayed higher catalytic activities as a result of the preferential exposure of {100} facets, which are the most active towards CO oxidation relative to {111} and {110}. Interestingly, the nanotubes with smooth surfaces also displayed higher catalytic activities when compared to the nanoshells, showing that the preferential exposure of {100} side facets compensated the decrease in their number of Pt surface atoms relative to the nanoshells. Our data showed that the catalytic performances were strongly dependent on the surface morphologies, in which the preferential exposure of more active surface facets may play a significant role in the optimization of performances relative to the number of Pt surface atoms.

Efeito do teor metálico em catalisadores Co/Al2O3 aplicados à reação de reforma a vapor de etanol

The development of cobalt catalysts to produce hydrogen from ethanol is the goal of this investigation. Co/Al2O3 catalysts were prepared by impregnation and characterized by atomic absorption, nitrogen adsorption, X-ray diffraction, Raman spectroscopy, temperature programmed reduction and carbon analysis. The catalysts contained Co3O4 oxide and Co3+ and Co2+ species interacting with alumina. The cobalt load affects the crystal size and the crystalline structure and higher Co loads influence the reaction mechanism, changing the selectivity of the catalysts, decreasing the amount of CO produced and avoiding the formation of products catalyzed by the support. The ethanol conversion was 50-70% with 10-<1% of CO in the hydrogen.

Síntese e caracterização de perovskitas LaNi(1-x)Co xO3 como precursores de catalisadores para a conversão do metano a gás de síntese pela reforma com CO2

LaNiO3 perovskite was modified by partial substitution of nickel by cobalt in order to increase the stability and resistance to carbon deposition during the methane CO2 reforming. The results showed that a suitable combination of precipitation and calcination steps resulted in oxides with the desired structure and with important properties for application in heterogeneous catalysis. The partial substitution of Ni by Co resulted in lower rates of conversion of both the reactants, but the catalyst stability was highly increased. The LaNi0.3Co0.7O3 catalyst, calcined at 800 oC, was the most active under the reaction conditions.

One-Pot Synthesis of Mesoporous Ni–Ti–Al Ternary Oxides: Highly Active and Selective Catalysts for Steam Reforming of Ethanol

One-pot synthesis of nanostructured ternary oxides of Ni, Al, and Ti was designed and performed via evaporation induced self-assembly (EISA). For the purpose of comparison, analogous oxides were also prepared by the impregnation method. The resulting materials were applied in two catalytic reactions: steam reforming of ethanol (SRE) for H2 production (subjected to prior activation with H2) and ethanol dehydration (ED; used without prior activation), to in situ analyze carbon accumulation by ethylene depletion when ethanol interacts with acidic sites present on the support. Modification of Ni-Al mixed oxides with titania was shown to have several benefits. CO2, NH3, and propylamine sorption data indicate a decrease in the strength of acidic and basic sites after addition of titania, which in turn slowed down the carbon accumulation during the ED reaction. These changes in interactions between ethanol and byproducts with the support led to different reaction pathways in SRE, indicating that the catalysts obtained by EISA with titania addition showed higher ethylene selectivity and CO2/CO ratios. The opposite was observed for the impregnated catalysts, which were less coke-stable during ED reactions and showed no ethylene selectivity in SRE. Carbon formed during ED reactions was shown to be thermodynamically less favorable and easier to decompose in the presence of titania. All catalysts studied displayed similar and high selectivities (∼80%) and yields (∼5.3 molH2/molethanol) toward H2, which place them among the most active and selective catalysts for SRE. These results indicate the importance of tailoring the support surface acidity to achieve high reforming performance and higher selectivity toward SRE, one of the key processes to produce cleaner and efficient fuels. For an efficient reforming process, the yield of byproducts is low but still they affect the catalyst stability in the long-run, thus this work may impact future studies toward development of near-zero coke catalysts.

Catalytic Properties of AgPt Nanoshells as a Function of Size: Larger Outer Diameters Lead to Improved Performances

We report herein a systematic investigation on the effect of the size of silver (Ag) nanoparticles employed as starting materials over the morphological features and catalytic performances of AgPt nanoshells produced by a combination of galvanic replacement between Ag and PtCl6(2-) and PtCl6(2-) reduction by hydroquinone. More specifically, we focused on Ag nanoparticles of four different sizes as starting materials, and found that the outer diameter, shell thickness, and the number of Pt surface atoms of the produced nanoshells increased with the size of the starting Ag nanoparticles. The produced AgPt nanoshells were supported into SiO2, and the catalytic performances of the AgPt/SiO2 nanocatalysts toward the gas-phase oxidation of benzene, toluene, and o-xylene (BTX oxidation) followed the order: AgPt 163 nm/SiO2 > AgPt 133 nm/SiO2 > AgPt 105 nm/SiO2 > AgPt 95 nm/SiO2. Interestingly, bigger AgPt nanoshell sizes lead to better catalytic performances in contrast to the intuitive prediction that particles having larger outer diameters tend to present poorer catalytic activities due to their lower surface to volume ratios as compared to smaller particles. This is in agreement with the H2 chemisorption results, and can be assigned to the increase in the Pt surface area with size due to the presence of smaller NPs islands at the surface of the nanoshells having larger outer diameters. This result indicates that, in addition to the overall diameters, the optimization of the surface morphology may play an important role over the optimization of catalytic activities in metal-based nanocatalysts, which can be even more pronounced that the size effect. Our data demonstrate that the control over surface morphology play a very important role relative to the effect of size to the optimization of catalytic performances in catalysts based on noble-metal nanostructures.