Catalytic Reduction of Aqueous Chlorate With MoO_x Immobilized on Pd/C

Abstract

Chlorate (ClO3 –) is an undesirable byproduct in the chlor-alkali process. It is also a heavily used chemical in various industrial and agricultural applications, making it a toxic water pollutant worldwide. Catalytic reduction of ClO3 – into Cl– by H2 is of great interest to both emission control and water purification, but platinum group metal catalysts are either sluggish or severely inhibited by halide anions. Here, we report on the facile preparation, robust performance, and mechanistic investigation of a MoO x –Pd/C catalyst for aqueous ClO3 – reduction. Under 1 atm H2 and room temperature, the Na2MoO4 precursor is rapidly immobilized from aqueous solution onto Pd/C as a mixture of low-valent Mo oxides. The catalyst enables complete reduction of ClO3 – in a wide concentration range (e.g., 1 μM to 1 M) into Cl–. The addition of Mo to Pd/C not only enhances the catalytic activity by >55-fold, but also provides strong resistance to concentrated salts. To probe the reaction mechanisms, we conducted a series of kinetic measurements, microscopic and X-ray spectroscopic characterizations, sorption experiments, tests with other oxyanion substrates, and a comparative study using dissolved Mo species. The catalytic sites are the reduced MoO x species (primarily MoIV), showing selective and proton-assisted reactivity with ClO3 –. This work demonstrates a great promise of using relatively abundant metals to expand the functionality of hydrogenation catalysts for environmental and energy applications.

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

“…S10). This short Mo−Mo distance, in comparison to the value of 3.4 Å in Mo VI oxide clusters (26), indicates the reduction of polymeric molybdate to Mo IV by Pd-activated H2 (19). The Mo−Mo coordination number (CN, 0.9 ± 0.5) suggests the heterogeneity of the surface Mo species as a mixture of monomers (CN = 0), dimers (CN = 1), and polymers (CN > 1).…”

“…Thus, the additional 4.5 wt% of Mo in a 5 wt% MoOx−Pd/C catalyst acted as the structural building block of polymeric MoOx clusters rather than catalytic sites. The CN for Mo−Mo in MoOx−Pd/C (1.7 ± 0.6, table S3) also indicated the dominance of polymeric MoOx clusters (19). In stark comparison, the ClO4 − reduction activity of [(NH2)2bpy]MoOx−Pd/C showed a linear increase until reaching 5 wt% of Mo.…”

Development of Nickel- and Magnetite-Promoted Carbonized Cellulose Bead-Supported Bimetallic Pd–Pt Catalysts for Hydrogenation of Chlorate Ions in Aqueous Solution

“…The elimination of chlorate ( ) from industrial process water is necessary not only from an environmental but also from an industrial point of view [ 1 , 2 , 3 , 4 ]. In the field of chlor-alkali electrolysis, the first membranes were introduced in the 1970s, which provided a more efficient ion-selective space-separation than the previously used diaphragm [ 5 ].…”

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

“…While enzymes use amino acid residues to facilitate the reduction of metal-bound oxyanions (10, 22), the carbon-supported catalyst needs external protons to enable the reaction (19,20). The optimal activity was afforded by 1 mM H + (pH 3.0 by H2SO4).…”

“…The poor EXAFS fittings including Mo−Pd bonding (tableS4) suggest isolated aggregation and distinct roles of Mo sites (OAT for ClOx − reduction) and Pd nanoparticles (electron transfer from H2). However, the hydrogenation reaction is necessary to transform the polymeric Mo VI precursors(19) and the free…”