Role of the Mg/Al atomic ratio in hydrotalcite-supported Pd/Sn catalysts for nitrate adsorption and hydrogenation reduction

Abstract

Hydrotalcite-supported Pd/Sn catalysts with different Mg/Al atomic ratios (2, 3, 4, and 5) for nitrate adsorption and hydrogenation reduction were successfully synthesized by a coprecipitation method. The results showed that different atomic ratios of Mg/Al resulted in different interlayer spacings and zetapotentials of the catalysts, which thus influenced its adsorption capacity. With the increase of Mg/Al atomic ratio, the interlayer spacing rose and zeta-potential decreased. The adsorption properties of the catalysts were mainly affected by interlayer spacing when Mg/Al atomic ratios increased from 2 to 4. However, when Mg/Al atomic ratios further increased from 4 to 5, there was a negative impact on the adsorption properties of zeta-potential. Also, the adsorption capacity of the catalysts for nitrate followed the order: Mg/Al = 2 < Mg/Al = 3 < Mg/Al = 5 < Mg/Al = 4. In the catalytic reduction process, the adsorbed nitrates were further reduced to nitrites that remained in the same position in catalysts, but some of superabundant nitrites were released into water as primary and unstable products. The concentration of released nitrites was in the reverse order of the adsorption capacity. The catalytic selectivity and activity of the catalysts for nitrate reduction had the same sequence as its adsorption capacity.

Efficient Nitrate Reduction in a Fluidized Electrochemical Reactor Promoted by Pd–Sn/AC Particles

“…However, physico-chemical processes, such as ionexchange, reverse osmosis and electrodialysis, produce concentrated brine that must be treated or disposed of, and biological denitrification of drinking water is limited due to concerns with pathogens, turbidity, and chlorine demand in the treated water. Catalytic reduction of nitrate, including chemical catalytic methods and electrochemical catalytic methods, is emerging as the most promising and flexible technique to solve this problem [8][9][10][11][12][13][14][15].…”

“…Palladium was found to be the most active and selective metal for the reduction of nitrate, but the reduction of nitrate required a second metal as a co-catalyst [9]. Pd-Cu, Pd-Sn and Pd-In coated on support materials such as Al 2 O 3 or hydrotalcite have been shown to reduce nitrate when added to a solution along with hydrogen as an electron donor [8][9][10][11][12][13][14][15]. The catalytic reduction results in the production of nitrogen (N 2 ) gas and NO 2 -as intermediates [15].…”

Study of a combined sulfur autotrophic with proton-exchange membrane electrodialytic denitrification technology: Sulfate control and pH balance

“…Since nitrate has a deleterious effect on human health and environment, processes for nitrate removal have gained attention in recent years (Kleinjans et al, 1991;Nolan et al, 1997). The conventional treatment methods used to remove nitrate are reverse osmosis (RO) (Brigita et al, 2009), ion exchange (IE) (Samatya et al, 2006), catalytic (Prüsse et al, 2000;Florence et al, 2001;Wan et al, 2009a) and biological (Anabela et al, 2000;Lucas et al, 2005;Liu and Koenig, 2002;Rezania et al, 2007) processes. There are some disadvantages with these methods that limit their application.…”

“…For instance, both RO and IE cannot transfer nitrate into harmless nitrogen but only concentrate nitrate from water to waste brine that may pose a disposal problem for afterwards treatment. For the new method of catalytic process, although complete or partial nitrate removal is reported by the researchers Prüsse et al (2000), Florence et al (2001) and Wan et al (2009a), formation of ammonia and nitrite along with nitrate reduction is an undesired consequence of this method. Besides, high costs and deactivation of catalysts limits its utilization.…”

Eliminación Catalítica De Nitratos en Continuo en Aguas Naturales

“…Los materiales laminares como las hidrotalcitas también se han utilizado como soportes catalíticos en esta reacción. Así se ha estudiado el uso de hidrotalcitas con distintas relaciones Mg/Al y con distintos metales, obteniéndose los mejores resultados con las hidrotalcitas de Mg/Al de relación 4 e impregnadas con Cu y Pd [56][57][58]77]. …”