Aluminosilicate-catalyzed electroreduction of nitrate anion—An approach through alkalinity analysis

Catalytic Activity of Porous Crystalline Aluminosilicates in Continuous Nitrate Removal via Electroreduction

“…Microporous Aluminosilicates (AS) are expected to act as electrodes due to surface charge-induced electro-conductivity and as bifunctional catalysts that induce beneficial moderate acidity and surface activity. This was explained in terms of buffering effects of the solid surface and acidic species in the aqueous media, as reported earlier [13,31]. Here, the AS surface should act as a trap for the NH 4 + cation resulting from the protonation of the generated ammoinia.…”

“…This has stimulated interest towards more eco-friendly routes that can process high nitrate concentrations with relatively low investment costs. Among these, nitrate electro-reduction is undoubtedly the most interesting alternative in this regard, more particularly when efficiently optimized for reducing the energy consumption or in the presence of nonpolluting and recyclable clay-based catalysts [12,13]. This process involves mainly cathodic reactions (Reactions 1-6) that convert nitrate anion into undesirable by-products such as nitrite and ammonia, but ultimalately into harmless nitrogen gas under optimal conditions [14].…”

“…Among various metals such as Cu [18], Sn [19], Ni [20], Ti [16,21], Fe [22], and Pb [23] tested as electrode materials, Cu cathodes turned out to be effective in nitrate electroreduction [18]. However, the general tendency is that combined metals such as Cu-Sn [24], Cu-Ni [16,25], Rh-Ni [18], Sn-Pd [21], Pt-Ir [26], Ag-Pd [22], Ag-Pt-Pd [22], Pd-Co-Cu alloy [27] and stainless steel [12,13] show higher activity and selectivity as compared to monometallic electrodes. Indeed, stainless steel electrodes allowed achieving nitrate removal yield exceeding 90% [12,13].…”

“…However, the general tendency is that combined metals such as Cu-Sn [24], Cu-Ni [16,25], Rh-Ni [18], Sn-Pd [21], Pt-Ir [26], Ag-Pd [22], Ag-Pt-Pd [22], Pd-Co-Cu alloy [27] and stainless steel [12,13] show higher activity and selectivity as compared to monometallic electrodes. Indeed, stainless steel electrodes allowed achieving nitrate removal yield exceeding 90% [12,13]. Pd/Cu electrodes with 15% Cu content showed significant activity and selectivity in the formation of ammonia [28].…”

“…The use of acids can be justified by the compensation of the unavoidable production of detrimental alkalinity that favorably shift equilibrium towards nitrate depletion (Reactions 6). However, acidic pH may also influence not only nitrate electroreduction [13,15] but also further protonation of the unavoidably generated ammonia and electro-conversion of free ammonium cation at the anode surface [29,30].…”