Juan Ángel Botas

Cobalt Doping of the MOF-5 Framework and Its Effect on Gas-Adsorption Properties

Partial isomorphic substitution of Zn in IRMOF metal clusters by cobalt ions is described for the first time. Specifically, different numbers of Co(2+) ions have been incorporated during solvothermal crystallization into the Zn-based MOF-5 (IRMOF-1) framework, which is one of the most studied MOF materials. The amount of Zn that can be substituted seems to be limited, being no more than 25% of total metal content, that is, no more than one Co atom inside every metal cluster formed by four transition-metal ions, on average. Several characterization techniques, including X-ray diffraction, DR UV-visible spectroscopy, N(2) adsorption isotherms, and thermogravimetrical analysis, strongly support the effective incorporation of Co into the material framework. As-synthesized CoMOF-5 has cobalt ions in octahedral coordination, changing to tetrahedral by simple evacuation, presumably by the removal of two diethylformamide molecules per Co ion. Moreover, the H(2), CH(4), and CO(2) uptake of MOF-5 materials systematically increases with the Co content, particularly at high pressure. Such an increase is moderate anyway, considering that Co is incorporated into unexposed metal sites that are less accessible to gas molecules.

Contribution of cerium/zirconium mixed oxides to the activity of a new generation of TWC

Abstract The catalytic activity of several cerium/zirconium mixed oxides for TWC applications has been investigated with the aim of optimising the Ce/Zr composition. Their catalytic activity was surprisingly high, considering that no noble metal was present in the composition, particularly for oxidation reactions (CO and C3H6), while their reduction activity was very small (NO). The specific activity of the mixed oxides for CO and C3H6 was found to be the contribution of the individual specific activity of the single oxides. The best activity in practice (lowest T0 and T50 and highest X773) was found for the mixed oxide with a Ce/Zr ratio of 80/20, as a combination of its high specific activity and the highest specific surface area.

Influence of water and hydrocarbon processed in feedstream on the three-way behaviour of platinum-alumina catalysts

Abstract The influence of water and the nature of the hydrocarbon -methane, ethylene, propene and 1-butene- processed in the feedstream on the three-way behaviour of a ceria-modified alumina supported platinum catalyst is investigated. Experiments were carried out with static feedstreams with air-to-fuel ratios between 14.13 and 15.17 as well as with oxidizing-reducing cycled feedstreams simulating the real automobile exhaust mixture. Conclusions are drawn on the importance of water-gas shift and steam reforming reactions and their relationship with inhibition self-poisoning effects of carbon monoxide and/or hydrocarbons. Comparison of data of the prepared catalyst and those obtained at the same operational conditions with two commercial catalysts, with only platinum/alumina and platinum-rhodium/ceria-alumina respectively, allows confirmation of the effects of ceria and establishes the role of rhodium when added to the catalyst.

Kinetic considerations of three-way catalysis in automobile exhaust converters

Abstract The activity of three-way catalysts is highly dependent on the reactants present in the automobile exhaust gases (CO, NO x , HC, O 2 , H 2 O, CO 2 , N 2 ) as well as their relative concentration. Thus, the influence of each reactant on the kinetic behavior of the whole mixture makes difficult to establish the accurate kinetics of the system. Activity experiments carried out close to the real operation conditions (GHSV, concentration, etc.) with a Pt/CeO 2 /Al 2 O 3 catalyst supplied data on the CO and HC oxidation and NO reduction reactions in environments formed by different reactant combinations (from binary mixtures to the whole mixture simulating the real conditions at the automobile converter). The obtained results have shown notable variations in the oxidation/reduction mechanisms depending on the presence (or absence) of components in the environment. The presence of water always promoted the three-way activity of the catalyst. The compensation effect applied to the CO, NO and HC conversions confirmed that kinetic expressions obtained with partial mixtures (not very close to the real converter environment) have only limited application for determining the whole kinetic scheme occurring in the automobile converters.

Synthesis of cordierite monolithic honeycomb by solid state reaction of precursor oxides

The synthesis of cordierite monolithic honeycombs by solid state reaction at high temperature of alumina, kaolin, talc and silica has been studied. The synthesized honeycombs have been characterized by DTA and XRD. The crystal composition of the samples have been observed to be very dependent on temperature and time of reaction. Thermal treatment of the monolithic precursors at 1400°C for 30 minutes allows formation of high purity cordierite with high crystallinity, maintaining the desired monolithic structure of the honeycombs.

Effects of redox thermal treatments and feedstream composition on the activity of Ce/Zr mixed oxides for TWC applications

Abstract The activity of cerium/zirconium mixed oxides for TWC applications submitted to different thermal treatments under oxidising, reducing and redox-cycled atmospheres has been investigated. The effect of each individual reactant in the reaction system has been studied using feedstreams in which some components had been removed and substituted by nitrogen. The conclusions extracted from the individual reactions have been used to describe the role and effect of each reactant when all the components are present in the feedstream, and to explain the differences observed in the catalytic performance after different treatments. Finally, a Ce/Zr mixed oxide composition has been proposed as the best support for TWC applications.

Advances in the design of ordered mesoporous materials for low-carbon catalytic hydrogen production

It is believed that hydrogen will play a relevant role as an energy vector in the near future, but in order to fulfil these expectations the development of economically feasible routes with limited CO2 emissions is required. In this respect, catalysis is crucial in most of the possible processes for hydrogen generation and, accordingly, improvement in the catalyst properties should have a significant impact on the efficiency of the production. In particular, ordered mesoporous materials of different chemical composition (oxides and non-oxides) possess a high potential for improving a variety of catalytic routes for the production of low-carbon hydrogen. The activity of this type of catalyst is frequently enhanced due to a combination of high surface area, low diffusion restrictions, and high dispersion of the supported active phases. In this work, we review the latest advances in the use of these mesostructured catalysts in the most relevant routes for hydrogen generation with reduced greenhouse emissions: steam reforming of biomass derived feedstocks (biogas, ethanol, and glycerol), methane and ammonia decomposition and photocatalytic reduction using sacrificial electron donors.

Comparative three-way behaviour of Pt, Pd and Rh single and combined phases in a full gas mixture with oscillating feedstream

ABSTRACT A series of palladium, platinum and rhodium (single and combined) catalysts supported on cerium-doped γ-alumina has been prepared. The monometallic catalysts were prepared by adsorption from the metal solution, and the multimetallic catalysts by joint adsorption as well as by physical mixture of those monometallic which allowed to obtain similar final metal composition. The three-way behaviour of the prepared catalysts has been tested with full synthetic gas mixtures composed of N 2 , CO 2 , CO, C 3 H 6 , NO, O 2 and H 2 O under reducing-oxidising cycled and stationary feedstream compositions.

HREM and XRD characterisation of thermal ageing of Pd/CeO2/Al2O3 automotive catalysts

A Pd/CeO2/Al2O3 catalyst is submitted to high temperature under oxidising, reducing and cycled oxidising/reducing feedstreams, and the activity of fresh and aged catalysts is analysed under simulated real conditions. The samples have been characterised by high resolution electron microscopy (HREM) and X-ray diffraction (XRD), and a correlation between the chemical structure of the catalyst and its catalytic behaviour is intended to be established.

TWC Behaviour of Platinum Supported on High and Low Surface Area Cerium/Zirconium Mixed Oxides

The catalytic activity as TWC of two Pt catalysts supported on one high and one low surface area Ce0.68Zr0.32O2 mixed oxide has been investigated. The catalyst behaviour was studied both fresh and after thermal ageing, and correlated to the textural and the Pt dispersion changes. The results show that the catalyst with the highest surface area is not necessarily the catalyst which has the best performances as TWC. The different behaviour of the catalysts has been attributed mainly to differences in the platinum dispersion and/or the reducibility of the samples, both related to the platinum/support interaction.