Miguel Laborde

Bio-ethanol steam reforming on Ni/Al2O3 catalyst

In this work, the ethanol steam reforming on Ni/γAl2O3 catalyst at temperatures between 573 and 773 K was studied and an overall reaction scheme as a function of temperature was proposed. It can be concluded that higher water/ethanol ratio (6:1) and higher temperature (773 K) promote hydrogen production (91% selectivity). Over Ni-based catalyst there would not be evidences that water gas shift reaction occurs. The presence of oxygen in the feed produces a favorable effect on carbon deposition; nevertheless the carbon monoxide production is not reduced.

Hydrogen production from steam reforming of bioethanol using Cu/Ni/K/γ-Al2O3 catalysts. Effect of Ni

Hydrogen to be used as a raw material in fuel cells or even as a direct fuel can be obtained from steam reforming of bioethanol. The key aim of this process is to maximize hydrogen production, discouraging at the same time those reactions leading to undesirable products, such as methane, acetaldehyde, diethyl ether or acetic acid, that compete with H2 for the hydrogen atoms. Cu–Ni–K/γ-Al2O3 catalysts are suitable for this reaction since they are able to produce acceptable amounts of hydrogen working at atmospheric pressure and a temperature of 300°C. The effect of nickel content in the catalyst on the steam-reforming reaction was analyzed. Nickel addition enhances ethanol gasification, increasing the gas yield and reducing acetaldehyde and acetic acid production.

Hydrogen from steam reforming of ethanol. characterization and performance of copper-nickel supported catalysts

Abstract The effect of the copper loading and calcination temperature on the structure and performance of Cu/Ni|K|γ-Al2O3 catalysts is examined. TPR, XRD and N2O chemisorption techniques are employed. Activity and selectivity measurements are carried out considering steam reforming of ethanol as the test reaction. The appearance of CuO phase depends on copper loading and calcination temperature, whereas NiAl2O4 phase is present in all the analyzed samples. Copper dispersion is favored at lower copper loading. TOF values indicate that steam reforming of ethanol should be a structure-sensitivity reaction, at least under the experimental conditions used in this work.

Activity and structure-sensitivity of the water-gas shift reaction over CuZnAl mixed oxide catalysts

Abstract The activity and structure-sensitivity of the water-gas shift (WGS) reaction over Cu Zn Al mixed oxide catalysts were studied. Three sets of samples with different Cu/Zn and (Cu+Zn)/Al atomic ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary hydroxycarbonate precursors contained hydrotalcite, aurichalcite and/or rosasite phases. The decomposed precursors contained CuO, ZnO, ZnAl 2 O 4 , and Al 2 O 3 . The relative proportion of these phases depended on both the chemical composition of the sample and the calcination temperature employed for decomposing the precursor. After activation with hydrogen, samples were tested for the WGS reaction at 503 K. The turnover frequency of the eighteen samples tested was essentially the same (0.2–0.3 s −1 ) irrespective of changing the copper metal surface area between 3 and 35 m 2 /g Cu and the metallic copper dispersion between 0.5 and 5.0%. This indicated that the WGS reaction is a structure-insensitive reaction, as the specific reaction rate r 0 (mol CO/h/g Cu) is always proportional to the copper metal surface area. Preparation of mixed oxides with a high copper dispersion is therefore required for obtaining more active catalysts. It was found that the value of the metallic copper dispersion is related to the amount of hydrotalcite contained in the hydroxycarbonate precursor: the higher the hydrotalcite content in the precursor, the higher the copper metal dispersion in the resulting catalyst and, as a consequence, the higher the catalyst activity. Ternary Cu/ZnO/Al 2 O 3 catalysts exhibited a substantially faster WGS activity than binary Cu/ZnO catalysts. The addition of aluminium, although inactive for the WGS reaction, is required for improving the catalyst performance.

Hydrogen production via catalytic gasification of ethanol. A mechanism proposal over copper–nickel catalysts

Ethanol gasification using Cu–Ni–K/γ-Al2O3 catalysts was studied. The reaction was carried out at a low temperature (300°C) and atmospheric pressure. The influence of the diffusional effects, the residence time and the water/ethanol molar ratio in the feed on the ethanol conversion and on the product distribution was analysed. Additional experiments were performed with monometallic catalysts, such as Cu–K/γ-Al2O3 and Ni–K/γ-Al2O3 catalysts. Ethanol gasification is favoured by a diminution of the diffusional resistances, high residence time and low water to ethanol feed ratio. A probable reaction mechanism is postulated, which is consistent with the experimental results and let identify the function of each metal (copper and nickel).

Hydrogen production from the low-temperature water-gas shift reaction : kinetics and simulation of the industrial reactor

Abstract The kinetics of the water-gas shift reaction (WGSR) over a copper/zinc oxide/alumina catalyst have been studied. The experiments were carried out at 453–503 K and atmospheric pressure. A reactive mixture of similar composition to that employed in the industrial process was used. An integral reactor, an integral procedure and a data treatment valid for near equilibrium conditions were employed. A number of representative models were examined. It was found that only a Langmuir-Hinshelwood model, which considers the adsorption of four species (CO, CO2, H2 and H2O) and the surface reaction as the controlling step, adequately describes the reaction behaviour at the temperature and concentration ranges investigated. Values of adsorption constants and adsorption heats for the four components involved in the WGSR are given. An algorithm for the simulation of an adiabatic fixed-bed reactor was developed with the aim of checking the kinetics expression. Both the industrial and simulated compositions agree. It is proved that the kinetic expression proposed which is in harmony with a Langmuir-Hinshelwood mechanism is useful in designing industrial low-temperature converters.

Solving differential equations with unsupervised neural networks

Abstract A recent method for solving differential equations using feedforward neural networks was applied to a non-steady fixed bed non-catalytic solid–gas reactor. As neural networks have universal approximation capabilities, it is possible to postulate them as solutions for a given DE problem that defines an unsupervised error. The training was performed using genetic algorithms and the gradient descent method. The solution was found with uniform accuracy (MSE ∼10−9) and the trained neural network provides a compact expression for the analytical solution over the entire finite domain. The problem was also solved with a traditional numerical method. In this case, solution is known only over a discrete grid of points and its computational complexity grows rapidly with the size of the grid. Although solutions in both cases are identical, the neural networks approach to the DE problem is qualitatively better since, once the network is trained, it allows instantaneous evaluation of solution at any desired number of points spending negligible computing time and memory.

Synthesis of acetal (1,1-diethoxyethane) from ethanol and acetaldehyde over acidic catalysts

Various acidic catalysts (zeolitic and amorphous FCC catalysts, mordenite, montmorillonite, and sulfonic ion exchange resin) were tested for the synthesis of acetal from ethanol and acetaldehyde, at 4 and 20°C and atmospheric pressure in batch stirred reactors. All the catalysts were active, but the exchange resin showed a much better performance than the other catalysts, since it quickly reached equilibrium ethanol conversion values. The resin was also tested under different pressures and catalyst to reactants ratios. Clear relationships between the catalyst activity, the amount of acidity and the physical properties of the catalysts were not apparent. A possible reaction mechanism suggests that protonic acid sites are necessary. Water, a reaction product, seems to have an inhibitory effect on the reaction rate.

Simulation of CO Preferential Oxidation (COPrOx) Monolithic Reactors

Abstract In this work, a COPrOx monolithic reactor with a CuO/CeO2/Al2O3 catalytic washcoat was modelled to purify a H2 stream for a 2 kW PEM fuel cell. Preliminary simulations included isothermal monoliths operating between 423 and 463 K, and the optimization of linear axial temperature profiles. For a fixed total system size and a desired CO outlet molar fraction lower than 20 ppm, an isothermal temperature profile maximized the global selectivity towards CO oxidation. Then, different schemes of adiabatic monoliths with interstage cooling were modelled and evaluated. It was found that wide operating temperature ranges lower the necessary number of stages, but decrease the global selectivity and rise system sensitivity to inlet temperatures. A 1D heterogeneous model was used to simulate the monoliths.

A novel catalyst system for ethanol gasification

Nickel/copper/chromium catalysts supported on porous alumina were synthesized. Samples of 4.0% Ni/0.75% Cu/0.25% Cr on α-Al2O3 were run in a fixed-bed reactor system dedicated to the steam reforming of ethanol. The operating temperatures ranged from 573 to 823 K, the water/ethanol mole ratios from 0.4 to 2.0 and the space velocities from 2.5 to 15 h−1. The data reveal high activity of this catalyst for ethanol gasification, as well as good selectivity in H2 and CO. Comparison of these results with thermodynamic equilibrium values indicate that the catalytic effect is more pronounced at lower temperatures.