New insight in the solid state characteristics, in the possible intermediates and on the reactivity of Pd–Cu and Pd–Sn catalysts, used in denitratation of drinking water

State-of-the-art and perspectives of the catalytic and electrocatalytic reduction of aqueous nitrates

“…In or Sn), determine the distance between active sites of palladium and noble metal, influencing the interactions between the reactants and the catalyst. The catalyst preparation protocol and the salt used also have a direct effect on the final size and distribution of the metallic particles over the support surface [60,66,91,96,105,106]. The catalytic behaviour in nitrate reduction experiments was affected by metal-metal and metal-support interactions that can be modified by the temperature of both the reduction and calcination steps [49,89,90,93].…”

“…Thus, a wide range of characterisation techniques have been used to report useful information, e.g. i) dispersion and composition of metal particles in the catalysts and supports are commonly described by X-ray diffraction techniques (XRD); ii) the specific surface area is calculated applying the BET method (SBET) to N2 adsorption isotherms; iii) the size distribution of the metallic particles is determined by transmission electron microscopy (TEM); iv) the metal content and elemental ratios of the catalysts are measured by X-ray fluorescence; v) X-ray photoelectron spectra (XPS) give information about the evolution of the oxidation and chemical state of the active phases and it is used to determine the binding energy of the different element core levels; vi) the average metal crystallite diameter and the metal dispersion in the reduced samples can be estimated from CO chemisorption with the double isotherm method; vii) H 2 pulse chemisorption measurements shows dispersion of palladium based on the hemispherical model and, viii) temperature-programmed reduction of hydrogen (H-TPR) is used to investigate the reducibility of the metals in the catalysts [53,65,106]. The results of many publications with different metal loadings and Pd:Me ratios were collected and are listed inTable 2.…”

Photoelectron-spectroscopic and reactivity investigation of thin Pd–Sn films prepared by magnetron sputtering

“…An idea of adding tin as a second metal to improve their properties can be related with excellent gas sensing properties of semiconductor gas sensors based on Pd-SnO 2 combination [4]. Bimetallic Pd-Sn catalysts are very important in many inorganic and organic chemical reactions like low-temperature CO oxidation [5][6][7], drinking water denitrification [8,9], toluene acetoxylation [10], hydrogenation of acetylene [11], crotonaldehyde [12], maleinahydride [13], etc. The role of tin in these catalysts is usually connected with modification of Pd dband strictly related with particle adsorption properties.…”

Nitrate reduction in water: Influence of the addition of a second metal on the performances of the Pd/CeO2 catalyst

“…The global reaction is the following: Starting from the work of Hörold et al [5], numerous studies have been aimed at the development of suitable catalysts for nitrate reduction [6][7][8][9][10]. The addition of a second metal such as copper [6,11], silver [12], tin [10,[13][14][15], indium [10,[16][17], or two metals [18] to a noble metal on various supports leads to an important change in its activity and product selectivity. The proposed mechanism involves a redox reaction between the promoter, in its reduced state, and nitrate, leading to intermediate nitrite or directly to nitrogen gas or ammonium ion, and to an oxidized form of the promoter [9].…”

“…These metals were chosen because they have demonstrated to yield to very active Pd-SM catalysts when deposited on alumina [6,7,12,13]. Pd-Cu catalysts are also very active for nitrate removal but they produce not only N 2 as gaseous product, but also to N 2 O [7], which is known to contribute to the greenhouse effect and to ozone layer depletion.…”