Novel catalytic and mechanistic studies on wastewater denitrification with hydrogen

Abstract

The present work reports up-to-date information regarding the reaction mechanism of the catalytic hydrogenation of nitrates in water media. In the present mechanistic study, an attempt is made, for the first time, to elucidate the crucial role of several catalysts and reaction parameters in the mechanism of the NO(3)(-)/H(2) reaction. Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed on supported Pd-Cu catalysts for the NO(3)(-)/H(2) and NO(3)(-)/H(2)/O(2) reactions. The latter experiments revealed that the formation and surface coverage of various adsorbed active intermediate N-species on the support or Pd/Cu metal surface is significantly favored in the presence of TiO(2) in the support mixture and in the presence of oxygen in the reaction's gaseous feed stream. The differences in the reactivity of these adsorbed N-species, found in the present work, adequately explain the large effect of the chemical composition of the support and the gas feed composition on catalyst behaviour (activity and selectivity). The present study leads to solid mechanistic evidence concerning the presence of a hydrogen spillover process from the metal to the support. Moreover, this study shows that Cu clusters are active sites for the reduction of nitrates to nitrites.

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

“…This fact was later confirmed by Theologides et al [48,113], who concluded that the production of ammonium could be decreased by up to three times when 20 vol% of air is added to the gas fed to the fixed bed catalytic reactor.…”

Recent Approaches in Mechanistic and Kinetic Studies of Catalytic Reactions Using SSITKA Technique

“…243 The results pointed out that both the presence of TiO 2 in the support and the presence of oxygen in the feed stream enhance the formation and adsorption of different active Nintermediates on the support or on the surface of Pd−Cu catalysts. In addition, it has been found that Cu clusters increase the reduction rate of nitrates.…”

New insights into the antimicrobial treatment of water on Ag‐supported solids

“…The actual metal loading of Ag/Al 2 O 3 was found to be 0.97 wt%, whereas its total surface area (BET) was found to be 194.3 m 2 g −1 . The Ag dispersion value was determined by a modified H 2 chemisorption method as 0.23 …”

“…The modification of the method was made in order to eliminate any possible hydrogen spillover phenomena, which are common in metal‐supported catalysts. The exact procedure followed is described in detail elsewhere …”

“…Ag dispersion of Ag/Al 2 O 3 was determined by a modified H 2 chemisorption method followed by temperature programmed desorption (TPD) according to the experimental procedures reported elsewhere. [19][20][21] The modification of the method was made in order to eliminate any possible hydrogen spillover phenomena, which are common in metal-supported catalysts. The exact procedure followed is described in detail elsewhere.…”