José M. Serra

Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor

Membranes to make benzene from methane Methane gas is expensive to ship. It is usually converted into carbon monoxide and hydrogen and then liquefied. This is economically feasible only on very large scales. Hence, methane produced in small amounts at remote locations is either burned or not extracted. A promising alternative is conversion to benzene and hydrogen with molybdenumzeolite catalysts. Unfortunately, these catalysts deactivate because of carbon buildup; plus, hydrogen has to be removed to drive the reaction forward. Morejudo et al. address both of these problems with a solid-state BaZrO3 membrane reactor that electrochemically removes hydrogen and supplies oxygen to suppress carbon buildup. Science, this issue p. 563 Electrochemical processes extract hydrogen and maintain catalyst activity through oxygen injection. Nonoxidative methane dehydroaromatization (MDA: 6CH4 ↔ C6H6 + 9H2) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke. We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability.

Discovery of new paraffin isomerization catalysts based on SO42−/ZrO2 and WOx/ZrO2 applying combinatorial techniques

Abstract Applying accelerated techniques for catalyst synthesis and testing and a stochastic experimental design, two catalytic systems based on SO42−/ZrO2 and WOx/ZrO2 were seen as active and selective for n-paraffin isomerization. After three optimization cycles, a new catalyst formulation based on promoted SO42−/ZrO2 with improved activity and selectivity has been found. Characterization of the best catalysts generated in each cycle has been done. Activity and selectivity of the best catalyst found has been tested in the isomerization of a simulated industrial feed composed by n-pentane, n-hexane and n-heptane. For the second best catalytic system, i.e. WOx/ZrO2, the influence of tungsten content, promotor (Ce), nature of the starting precursor salt (sulfate, nitrate or chloride), and catalyst calcination temperature was studied using a factorial design. The relevance of the interaction between salt precursor and calcination temperature is discussed.

Enhanced H2 Separation through Mixed Proton–Electron Conducting Membranes Based on La5.5W0.8M0.2O11.25−δ

La(5.5) WO11.25-δ is a proton-conducting oxide that shows high protonic conductivity, sufficient electronic conductivity, and stability in moist CO2 environments. However, the H2 flows achieved to date when using La(5.5) WO11.25-δ membranes are still below the threshold for practical application in industrial processes. With the aim of improving the H2 flow obtained with this material, La(5.5) WO11.25-δ was doped in the W position by using Re and Mo; the chosen stoichiometry was La(5.5) W0.8 M0.2 O11.25-δ . This work presents the electrochemical characterization of these two compounds under reducing conditions, the H2 separation properties, as well as the influence of the H2 concentration in the feed stream, degree of humidification, and operating temperature. Doping with both Re and Mo enabled the magnitude of H2 permeation to be enhanced, reaching unrivaled values of up to 0.095 mL min(-1) cm(-2) at 700 °C for a La(5.5) W0.8 Re0.2 O11.25-δ membrane (760 μm thick). The spent membranes were investigated by using XRD, SEM, and TEM on focused-ion beam lamellas. Furthermore, the stability in CO2 -rich and H2 S-containing atmospheres was evaluated, and the compounds were shown to be stable in the atmospheres studied.

Styrene from toluene by combinatorial catalysis

The side-chain alkylation of toluene with methanol is one alternative technology to produce styrene that has been given attention in the last few years. In the literature basic materials has been proposed as catalyst for the reaction but the real number of tested catalysts is very small and few preparation parameters have been taken into account. In this work a combinatorial approach has been used to explore the possibilities of basic zeolites to carry out such reaction. To do this, the following catalyst variables have been studied: nature of zeolite, framework composition, nature and content of compensating cation and method of incorporation (exchange, impregnation). The results obtained confirm the requirements of both basic and acid sites in the catalysts and show the compromise between these two functions. The study carried out shows that zeolite-based catalysts are still poor reactive to give the styrene/ethylbenzene yields required for converting this process in a real alternative to the existing one, based on the alkylation of benzene with ethylene, followed by the dehydrogenation of ethylbenzene to styrene.

Development of a low temperature light paraffin isomerization catalysts with improved resistance to water and sulphur by combinatorial methods

By means of combinatorial techniques (high-throughput catalyst preparation and testing systems, and a genetic algorithm (GA)), a search of new more tioresistant catalysts for low temperature isomerization of light paraffins has been conducted. After three evolving cycles catalysts have been found that not only are active and selective but also are more resistant to deactivation by water and sulphur than the corresponding conventional ones. The results have been reproduced in a pilot plant and the stability is shown.

Application of Artificial Neural Networks to Combinatorial Catalysis: Modeling and Predicting ODHE Catalysts

This paper shows how artificial neural networks are useful for modeling catalytic data from combinatorial catalysis and for predicting new potential catalyst compositions for the oxidative dehydrogenation of ethane (ODHE). The training and testing sets of data used for the neural network studies were obtained by means of a combinatorial approach search, which employs an evolutionary optimization strategy. Input and output variables of the neural network include the molar composition of thirteen different elements presented in the catalyst and five catalytic performances (C2H6 and O2 conversion, C2H4 yield, and C2H4, CO2, and CO selectivity). The fitting results indicate that neural networks can be useful in high-dimensional data management within combinatorial catalysis search procedures, since neural networks allow the ab initio evaluation of the reactivity of multicomponent catalysts.

Outstanding hydrogen permeation through CO2-stable dual-phase ceramic membranes

Mixed electronic- and protonic-conducting composites made up of physical mixtures of La5.5WO11.25−δ–La0.87Sr0.13CrO3−δ (LWO–LSC) have been evaluated as H2 separation membranes for operation at temperatures greater than 550 °C. The mixture of these two ion-conducting phases led to non-linear synergetic effects; i.e. unexpected enhancement of the total conductivity and well-balanced ambipolar conductivity, resulting in appealing H2 permeation fluxes through robust ceramic membranes. The preparation, primary characterization, H2 permeation and stability studies of various composites is presented. Mixing LWO and LSC phases makes it possible (1) to improve the LSC sintering behavior and to achieve very high membrane densities and (2) to obtain compounds with high total conductivity, higher than that shown for LWO and LSC, separately. The highest permeation rate is achieved for the 50 vol%-LWO–LSC membrane, though other composite compositions showed higher total conductivity. Moreover, the influence on the H2 permeation of the composite composition, the humidification of gas streams, temperature and the use of various catalytic coatings on the membrane surface is evaluated. The nature of the transport mechanism is investigated by the permeation studies using deuterium tracers. The H2 permeation rates reported in this investigation for a 370 μm thick 50 vol%-LWO–LSC membrane, e.g. 0.15 mL min−1 cm−2 at 700 °C, are the highest reported values, up to date, for any bulk mixed protonic-electronic membranes. The H2 permeation magnitude achieved at moderate temperatures along with the proven stability in CO2-rich atmospheres are firm steps towards the future application of this type of membrane for industrial processes.

Can artificial neural networks help the experimentation in catalysis

This work is focused on the practical application of artificial intelligent techniques in chemical engineering. Specifically, it describes an application of artificial neural networks for modelling the kinetics of a chemical reaction using methods not based in a kinetic model. Thus, neural networks have been used to model the behaviour of one catalyst under different reaction conditions for a specific reaction, i.e. n-octane isomerisation. Secondly, trained neural networks were used to model successfully another reaction with a similar reaction network.

Screening of A-Substitution in the System A0.68Sr0.3Fe0.8Co0.2O3 − δ for SOFC Cathodes

Several elements were studied as potential A-site substituents in the perovskite A 0.68 Sr 0.3 Fe 0.8 Co 0.2 O 3-δ system. The considered elements included La, Pr, Sm, Nd, Er, Eu, Gd, Dy, and Ba. The multicomponent oxides were prepared following a complexation-polymerization-pyrolysis method. The materials were characterized by X-ray diffraction, thermal dilatometry, and electrical conductivity under different oxidant atmospheres. The obtained materials were studied as solid oxide fuel cell cathodes, preparing porous films on top anode-supported cells with a yttria-stabilized zirconia electrolyte and a CGO protective layer. The complete cell was characterized by direct current voltamperometry using air and wet H 2 as fuel, whereas the porosity of the layer was studied by gas diffusion experiments after electrochemical testing. Oxygen conduction was investigated on gastight membranes prepared for La- and Pr-based materials under flow of air and helium (sweep) in the range from 650 to 1000°C. Pure perovskite structure was not obtained for the cations with the smallest ionic radii. The materials with the best electrochemical performance at 650°C contained Pr, Sm, La, and Ba. The good electrochemical performance seems to be principally related to the intrinsic electrocatalytic properties of the material (perovskite or small clusters of the single oxide) because no clear correlations of the electrochemical performance and ionic conductivity, electronic conductivity, or gas diffusivity could be found. The electrochemical performance at 650°C could be correlated with the catalytic activity for methane oxidation in a fixed bed reactor in the same temperature range. Finally, the catalytic promotion of a Pr-containing perovskite was evaluated by impregnation with Pd.

Enhancing oxygen permeation through hierarchically-structured perovskite membranes elaborated by freeze-casting

Innovative asymmetric oxygen-transport membrane architectures were prepared by combining freeze-casting and film deposition techniques. Freeze-casting enabled the optimization of the gas transport through the support by creating a hierarchical porosity while a dense top-layer of 30 μm was coated over this support by screen printing. The versatility of this technique was demonstrated by preparing highly porous bodies made of fast ionic conductors, e.g. perovskites and doped ceria fluorites, with a large number of applications in catalysis, electrochemistry and gas separation. Permeation tests using an all-La0.6Sr0.4Co0.2Fe0.8O3−δ asymmetric membrane proved the beneficial effect of such porous supports over the O2 fluxes with a maximum value of 6.8 mL min−1 cm−2 at 1000 °C, markedly above the results achieved so far with conventional preparation techniques. Gas permeance study through the porous freeze-cast support showed that the particular pore structure allows the gaseous transport resistance to be minimized. The related pressure drop is found to be very low in comparison with conventional porous supports, e.g. tape-cast supports, with for example only 0.59 bar mm−1 with argon at 800 °C for an inlet flow of 400 mL min−1 cm−2. Finally, the stability of the asymmetric membrane has been evaluated under CO2 atmosphere during 48 hours and at 900 °C. The membrane is found to be stable without deactivation nor decrease in the O2 permeation flux.