Catalytic reduction of nitrate and nitrite ions by hydrogen: investigation of the reaction mechanism over Pd and Pd–Cu catalysts

Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

“…This result indicated that the catalyst was not corroded during the reaction with N 2 H 4 in a highly concentrated NO 3 7 solution. The mechanism of NO 3 7 reduction with Pd-Cu catalysts and H 2 has been widely studied, and it has been deduced that NO 3 7 is reduced through NO 2 7 to N 2 , N 2 O, and NH 3 via reaction with hydrogen adsorbed on the catalyst surface [6,11,14,16,17]. In the present study, a Pd-Cu catalyst was also used, and N 2 , N 2 O, and NH 3 were produced.…”

“…These results clarified that Cu is indispensable for the reduction of NO 3 7 . It has been reported that the reduction of NO 3 7 to NO 2 7 is initiated by the Cu sites, which are then converted to Cu 2 O during the deoxidation of NO 3 7 [14]. However, the formed Cu 2 O must then be reduced back to Cu by the spillover hydrogen generated mainly on the Pd sites, thus regenerating the Pd-Cu alloy.…”

“…Therefore, a nitrate removal method is required to efficiently remove NO 3 7 of high concentration from a large amount of waste and reduce the amount of radioactive waste produced. It has been reported that NO 3 7 is reduced via a catalytic reduction method using a bi-metal catalyst such as palladium-copper (Pd-Cu) and a reductant such as hydrogen gas (H 2 ) [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], and this method has a possibility of meeting such requirements. However, because this method was mainly studied for the denitration of low-concentrated nitrate salt solutions, the applicability of the method to the denitration of highly concentrated nitrate salt solutions must be confirmed.…”

“…Since Vorlop and Tacke [4] reported a reduction method for low concentrations of NO 3 7 using supported Pd-Cu as the catalyst and H 2 as the reductant, many studies have been conducted [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The mechanism of NO 3 7 reduction with a Pd-Cu catalyst and H 2 reductant has been studied, and it was deduced that NO 3 7 is reduced through the nitrite ion (NO 2 7 ) to nitrous oxide (N 2 O), nitrogen (N 2 ), or ammonia (NH 3 ) via hydrogen adsorbed on the catalyst surface [6,11,14,16,17].…”

“…The mechanism of NO 3 7 reduction with a Pd-Cu catalyst and H 2 reductant has been studied, and it was deduced that NO 3 7 is reduced through the nitrite ion (NO 2 7 ) to nitrous oxide (N 2 O), nitrogen (N 2 ), or ammonia (NH 3 ) via hydrogen adsorbed on the catalyst surface [6,11,14,16,17]. Ilinitch et al [14] reported that the maximum reaction rate for NO 3 7 was achieved using a catalyst with a molar ratio of Pd:Cu ¼ 1:0.8, and that the maximum reaction rate of NO 2 7 was observed with a Pd monometallic catalyst.…”