A study of different supports for the catalytic reduction of nitrates from natural water with a continuous reactor

Abstract

The aim of this work is to study the activity for the nitrate catalytic reduction in natural water, using a continuous stirred tank reactor, of Pd/Cu and Pd/Sn catalysts supported on different materials. The studied supports are: -Al 2 O 3 (commercial), active carbon, graphite, hydrotalcite and alumina synthesized in our laboratory with a high surface area. The activity and selectivity of the catalysts supported on these materials have been compared. The best results have been obtained with the Pd/Sn catalysts supported on alumina. These results show that the surface area of the support is not the only important characteristic for an active catalyst in this reaction, being also very significant its acid-base properties, its electrical conductivity and its interaction with the metallic active sites. The adequate combination of these characteristics is necessary to obtain an active catalyst. The influence of the Pd/Sn content on the activity of the alumina supported catalysts was studied, observing that the best activity was obtained when the Pd/Sn ratio was higher than 1. This result clearly indicates that it is necessary to have both Pd and Pd-Sn centers in order to obtain an active catalyst.

Tin-palladium supported on alumina as a highly active and selective catalyst for hydrogenation of nitrate in actual groundwater polluted with nitrate

“…Among Pd-based bimetallic catalysts, Cu-Pd ones have been the most extensively studied because of their high activity and selectivity. [6][7][8][9][10][11][12][13][14][15][16][17][18]23,24,[27][28][29][30][31][32][33][34] In most studies on Cu-Pd catalysts, the catalytic performances were evaluated in distilled or deionized water, in which nitrate (MNO3, M = Na or K) was dissolved, and some Evaluation of the catalytic performances in groundwater is a necessary consideration for practical applications of this catalytic purification technology because coexisting matter in groundwater, including cations, anions, and water-soluble organic compounds, affects the catalytic performance. In some studies, Cu-Pd catalysts have been used for the reaction in actual groundwater, natural water and tap water samples.…”

“…In some studies, Cu-Pd catalysts have been used for the reaction in actual groundwater, natural water and tap water samples. 23,[29][30][31]36 However, substantial decreases in the performance of the Cu-Pd catalysts have been observed in those water samples, although the catalysts exhibited good performance in distilled or deionized water. 29,31 Pintar et al have compared the catalytic performance of Cu-Pd/Al2O3 in tap water with that in aqueous NO3solutions and pointed out that hydrogen carbonate (HCO3 -) in tap water causes a decrease in the catalytic performance.…”

“…32 Sulfate ion and its reduced products, including SO3 2and HS -, formed under the reaction conditions, greatly decrease the reaction rate for NO3reduction over supported Cu-Pd catalysts. 32,37 Pd-based bimetallic catalysts, other than Cu-Pd, including Sn-Pd [19][20][21][22][23][24][27][28][29]34,35 and In-Pd [24][25][26][27][28]34 show activity towards the hydrogenation of NO3 -. The base metal sites in these catalysts have different affinities for coexisting ions in water from those of the Cu sites in Cu-Pd catalysts, and thus, the catalysts have strong potential to deliver superior performance in groundwater than Cu-Pd catalysts do.…”

Nitrate Catalytic Reduction over Bimetallic Catalysts: Catalyst Optimization

“…Different metal loadings were considered to optimize the ratio of the two metals. Thus, in the first stage, a content of 1 wt% for both promoter and noble metals was considered, and for the most active supports, a content of 5 wt% of palladium and 2.5 wt% of copper was adopted [17,32].…”

NOx selective catalytic reduction at high temperatures with mixed oxides derived from layered double hydroxides

“…Nevertheless these additives must be able to operate at the high temperatures found in the FCC regenerator (around 700-750ºC), and in the presence of other gases such as CO, SO 2 , CO 2 , hydrocarbons, O 2 and H 2 O [5][6]. In these conditions, the common catalysts used for the NO x selective catalytic reduction or decomposition such as metal exchanged zeolites [7], modified pillared clays [8] or promoted V catalysts [9][10][11] are not stable enough and other alternatives should be explored.…”