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5. Conditional Equilibrium Constants Reviewed.

Author

Rodríguez de San Miguel, Eduardo, González-Albarrán, René, and Rojas-Challa, Yahsé

Subjects
EQUILIBRIUM, SPECIATION analysis, ACTIVITY coefficients, EQUILIBRIUM reactions, ANALYTICAL chemistry, CHEMICAL speciation
Abstract

A free energy-based conceptual theoretical framework from which the conditional equilibrium constant can be comprehensibly understood is presented. This constant is found to be a weighted geometric mean of the equilibrium constants of the reactions of all forms of the conditioned species under buffering conditions, where the weight is given by a function of their predominance in terms of their mole fractions. Once it is shown that this type of equilibrium constant can be easily deduced form free energy functions, it is shown how corrections for activity coefficient can be incorporated as well. The framework additionally permits to interpret side-reactions coefficients as free energy terms related to the chemical speciation of the system, allowing the use of the generalization of Hess' law to obtain conditional constants and a straightforward deduction of multiconditional equilibrium constants. Furthermore, different uses of the conditional constants along the actual literature are reviewed as well allowing to have a complete and updated panorama of the employment of this important concept in chemical and speciation analysis in many areas of research. [ABSTRACT FROM AUTHOR]

Published
2023
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10. An egg-shell bifunctional CeO2-modified NiPd/Al2O3catalyst for petrochemical processes involving selective hydrogenation and hydroisomerization

Author

Méndez, Franklin J., Alves, Javier A., Rojas-Challa, Yahsé, Corona, Oscar, Villasana, Yanet, Guerra, Julia, García-Colli, Germán, Martínez, Osvaldo M., and Brito, Joaquín L.

Abstract

The catalytic performance during the 1-butyne hydrogenation using two reduced Al2O3-supported Pd-based catalysts was carried out in a total recirculation system with an external fixed-bed reactor. The lab-prepared egg-shell NiPd/CeO2-Al2O3catalyst (NiPdCe) with Pd loading = 0.5 wt%, Ni/Pd atomic ratio = 1 and CeO2loading = 3 wt% was synthesized and characterized, and it was compared with an egg-shell Al2O3-supported Pd based commercial catalyst (PdCC). The reduced catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The textural characteristics and ammonia temperature-programmed desorption profiles of the fresh (unreduced) catalysts were also obtained. Both catalysts show high 1-butyne conversion and selectivity to 1-butene, but the catalysts also present important differences between hydroisomerizing and hydrogenating capabilities. NiPdCe catalyst shows higher capability for hydroisomerization reactions, while the PdCC catalyst exhibits higher hydrogenating capability. The observed catalytic performances can be interesting for some industrial processes and can provide a guideline for the development of a Pd-based catalyst with specific catalytic properties.

Published
2021
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