Impact of Na+ and Ca2+ Cations on the Adsorption of H2S on Binder-Free LTA Zeolites

Hydrogen sulfide is removed from natural gas via adsorption on zeolites. The process operates very effectively, but there is still potential for improvement. Therefore, in this article, the adsorption of hydrogen sulfide was investigated on eight LTA zeolites with different cation compositions. Starting with the zeolite NaA (4 A), which contains only Na+ cations, the Ca2+ cation content was gradually increased by ion exchange. Equilibrium isotherms from cumulative breakthrough curve experiments in a fixed-bed adsorber at 25°C and 85°C at 1.3 bar (abs.) were determined in the trace range up to a concentration of 2000 ppmmol. From a comparison of the isotherms of the different materials, a mechanistic proposal for the adsorption is developed, taking into account the specific positions of the cations in the zeolite lattice when the degree of exchange is increased. The shape of the isotherms indicates two energetically different types of adsorption sites. It is assumed that two mechanisms are superimposed: a chemisorptive mechanism with dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice and a physisorptive mechanism by electrostatic interaction with the cations in the lattice. As the degree of exchange increases, the proportion of chemisorption sites seems to decrease. Above an exchange degree of 50%, only evidence of physisorption can be found. It is shown that this finding points to the involvement of weakly bound sodium cations at cation position III in the chemisorption of hydrogen sulfide.

Co-Exchange of Mn: A Simple Method to Improve Both the Hydrothermal Stability and Activity of Cu–SSZ-13 NH3–SCR Catalysts

A series of Cu–Mn–SSZ-13 catalysts were obtained by co-exchange of Mn and Cu into SSZ-13 together (ion exchange under a mixed solution of Cu(NO3)2 and Mn(NO3)2) and compared with Cu–SSZ-13 catalysts on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia. The effects of total ion exchange degree and the effect of Mn species on the structure and performance of catalysts before and after hydrothermal aging were studied. All fresh and aged catalysts were characterized with several methods including temperature-programmed desorption with NH3 (NH3-TPD), X-ray diffraction (XRD), 27Al and 29Si solid-state nuclear magnetic resonance (NMR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and low-temperature N2 adsorption–desorption techniques. The results showed that the increase of the total ion exchange degree can reduce the content of residual Brønsted acid sites of catalysts, thus relieved the dealumination and the decrease of crystallinity of the catalyst during hydrothermal aging. The moderate addition of a Mn component in Cu–Mn–SSZ-13 catalysts significantly increased the activity of NO conversion at low temperature range. The selected Cu(0.2)Mn(0.1)–SSZ-13 catalyst achieved a high NO conversion of >90% in the wide and low temperature range of 175–525 °C and also exhibited good N2 selectivity and excellent hydrothermal stability, which was related to the inhibition of the Mn component on the aggregation of Cu species and the pore destruction of the catalyst during hydrothermal aging.

Resultados cambiarios y su relación con el grado de internacionalización de las empresas de la Bolsa Mexicana de Valores

Objetivo: El presente trabajo evalúa la relación existente del grado de internacionalización y el apalancamiento en moneda extranjera de las empresas de la Bolsa Mexicana de Valores (BMV) en la obtención de los resultados financieros cambiarios derivados de la volatilidad del peso mexicano. Metodología: las variables explicativas fueron el grado de internacionalización calificado por el número de países con los que realizan operaciones cada una de las compañías y el múltiplo de ventas en divisa extranjera y el apalancamiento medido por el múltiplo de pasivos en moneda extranjera; la variable explicada fue el importe de las ganancias y/o pérdidas cambiaras registradas en los reportes financieros corporativos por el periodo de 1990-2015 y se utilizó una regresión lineal múltiple para probar estadísticamente las hipótesis. Resultados: se encontró que estadísticamente la variable que mide el nivel de pasivos en moneda extranjera es la que principalmente determina las ganancias y/o perdidas cambiaras y en segundo lugar la proporción de ventas en moneda extranjera y en menor importancia el número de países con los que cada empresa desarrolla negocios. Conclusión: el 65% del total de las empresas de la BMV obtuvieron utilidades cambiarias, y además de los factores analizados en esta investigación, existen otros elementos que influyen en la obtención de los resultados cambiarios, es el caso los esquemas de cobertura utilizados por las compañías de la BMV. Palabras clave: Bolsa Mexicana de Valores, grado de internacionalización, ResultadoscambiariosAbstractObjective: The present study assesses the relationship between the degree of internationalization and the foreign currency leverage of the companies of the Mexican Stock Exchange (BMV) in obtaining exchange rate financial results derived from Mexican peso volatility. Methodology: the explanatory variables were the degree of internationalization qualified by the number of countries with which each company carries out operations and the multiple of sales in foreign currency and the leverage measured by the multiple of liabilities in foreign currency; the variable explained was the amount of exchange gains and / or losses recorded in the corporate financial reports for the period 1990-2015 and a multiple linear regression was used to test the hypotheses statistically. Results: it was found that statistically the variable that measures the level of liabilities in foreign currency is the one that mainly determines the exchange gains and / or losses and secondly the proportion of sales in foreign currency and, less importantly, the number of countries with the That every company develops business. Conclusion: 65% of all the companies of the BMV obtained exchange earnings, and in addition to the factors analyzed in this investigation, there are other elements that influence the obtaining of the exchange results, is the case the coverage schemes used by the Companies of the BMV.Keywords: Mexican Stock Exchange, degree of internationalization, Foreign exchangeresults.