J.A. Calles

Comparison of molecular simulation of adsorption with experiment

Experimental measurements of adsorption yield the surface excess. The Gibbs surface excess is the actual or absolute amount of gas contained in the pores less the amount of gas that would be present in the pores in the absence of gas-solid intermolecular forces. Molecular simulation of adsorption yields the absolute amount adsorbed. Comparison of simulated adsorption isotherms and heats of adsorption with experiment requires a conversion from absolute to excess variables. Molecular simulations of adsorption of methane in slit pores at room temperature show large differences between absolute and excess adsorption. The difference between absolute and excess adsorption may be ignored when the pore volume of the adsorbent is negligible compared to the adsorption second virial coefficient (V≪B1s).

Bifunctional catalyst NiHZSM-5: effects of the nickel incorporation method

Abstract The influence of the method used for the metal incorporation, technique and precursor compound on the hydroisomerization of n-decane over the bifunctional Ni HZSM -5 catalyst was studied. Two preparation methods, ion exchange and impregnation, using different nickel precursors were tested. Temperature-programmed desorption of ammonia (TPDA), thermogravimetric analyses (TGA), temperature-programmed reduction (TPR), electronic microscopy (SEM, TEM) and atomic absorption spectroscopy (AA) techniques were used to characterize the catalysts. The n-decane hydroisomerization was selected as a test reaction to determine the catalyst activity. These experiments were carried out in a basket type reactor, using a catalyst ground with sodium montmorillonite. The method of nickel incorporation was found to be an important indicator for the activity and selectivity of the catalyst, having a significant influence not only on its hydrogenating properties but also on its acidity. The nickel incorporation technique was mainly affecting the nickel dispersion, while it was affecting both functions, metallic and acid, when the precursor was modified.

Acidity modification during the agglomeration of ZSM-5 with montmorillonite

Abstract Ammonia TPD analyses of ZSM-5 zeolites of three Si/Al ratios (15, 30, 43) agglomerated with sodium montmorillonite revealed a noticeable modification on the acid properties of the bound zeolites as compared with the raw materials. An initial increase of the proportion of the weak acidity was found on the agglomerated zeolites, though the total and strong acidity decreases. The higher the Si/Al ratio of the zeolite, the higher is this increase. After several steps of ion exchange of the bound zeolites, the acidity reaches the expected values again, and the total and strong acidities are enhanced at the expense of the weak acidity. These results were related to a solid-state ion exchange between protons of the zeolite and cations of the clay during the calcination subsequent to the agglomeration.

Review of Supported Pd-Based Membranes Preparation by Electroless Plating for Ultra-Pure Hydrogen Production

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.

Binary and Ternary Adsorption Equilibria at High Pressure on Molecular Sieves

Adsorption isotherms of binary and ternary mixtures of CO2, ethylene and ethane have been experimentally obtained on a commercial carbon molecular sieve 5A, CMS, (up to 1500 kPa) and on a commercial 5A zeolite (up to 3000 kPa) at 293 K. Some strong equilibrium displacement effects and large deviations from ideal behaviour (including azeotropes) were observed on the adsorption on 5A zeolite, whereas the CMS does not show this behavior. This difference between both adsorbents can be explained in terms of their structure and chemical compositions. Moreover, the equilibrium data have been reproduced and predicted by thermodynamic models like IAS, HIAS, RAS and SPD, modified by introducing fugacity coefficients in the Raoult’s law. The results obtained by RAS and SPD models are practically similar and better than the other ones, particularly for the non-ideal systems on 5A zeolite.