Hydrodenitrification with PdCu Catalysts: Catalyst Optimization by Experimental and Quantum Chemical Approaches

Abstract

A continuous process for nitrate and nitrite abatement from drinking water by catalytic hydrogenation has been developed in our lab. We describe the experimental process development procedure, and support it with semiempirical quantum chemical methods. Comparisons of activated carbon (ACC) and silica glass fiber (GFC) cloths as supports for mono‐ and bimetallic Pd‐Cu catalysts show the former to be 45‐fold and 15‐fold more active for nitrite and nitrate hydrogenation, respectively, than the latter. Catalysts prepared by selective deposition of Cu on Pd/ACC led to better activity for nitrate hydrogenation than catalysts prepared by co‐impregnation or ion exchange methods. The optimal Cu:Pd atomic ratio was found to be 1:2. The computational results show the following: (i) The dispersion of Pd catalysts supported on ACC is much higher than that on GFC due to the larger surface area and higher density of adsorption sites, and that accounts for the higher activity of PdCu/ACC; (ii) Nanosized Pd particles supported on ACC have a semispherical shape and possess preferentially close‐packed triangular surfaces, while Pd/GFC particles are extended in the direction parallel to the support surface and show both fcc (100) and (111) planes; (iii) The interaction of Cu atoms with both supports is stronger than that of Pd; adsorbed Cu atoms show a greater ability to form monometallic than bimetallic bonds and that should result in poor mixing of the metal upon co‐impregnation, as was observed experimentally; (iv) Cu atoms in bimetallic PdCu particles admit a significant positive charge; the experimentally measured solubility of metal atoms correlates with their calculated charges. The best catalyst (2 wt%Pd‐0.6 wt%Cu/ACC) was employed in a novel continuous flow reactor for nitrate hydrogenation in distilled and tap water. The advantages of the reactor investigated over a conventional packed bed reactor are discussed, suggesting a potential for further process intensification.

Coordination-Resolved Electron Spectrometrics

“…421 AgPd is a good candidate for hydrogenation and permeation. 85,422 In the process of catalytic reaction, the direction and the ability of charge flow between the catalyst and the gaseous adsorbate are the key concern. The reactivity depends on the filling degree of the empty antibonding states of the catalyst by the reactant electrons.…”

Density Functional Theory Analysis of Dichloromethane and Hydrogen Interaction with Pd Clusters: First Step to Simulate Catalytic Hydrodechlorination

“…38,41,42 (iii) The interactions of the Pd particles with AC used as support. 43 It was found that Pd atoms interact more effectively with the defects (unsaturated carbons) on the surface of AC than with graphitic layers. Also, it was found that the Pd clusters tend to form small pseudospherical particles, with structures determined by triangular faces, which interact effectively with accessible sites (unsaturated carbon atoms) of AC, justifying the high dispersion of Pd on the surface of this support and the preference for being selectively adsorbed in narrow pores.…”

A Facile One‐Pot Synthesis and Enhanced Formic Acid Oxidation of Monodisperse Pd–Cu Nanocatalysts

“…Among the various bimetallic NPs, Pd-Cu NPs have been intensively explored as catalytic materials for a variety of reactions such as hydrogenation, combustion, and CO oxidation. [8][9][10] Moreover, such noble metal-non-noble-metal alloy NPs might be the best alternative economical catalyst with desired performance. [11,12] Recently, it has been reported that carbon-supported Pd-Cu NPs showed high activity for oxygen-reduction reactions (ORRs).…”