Nitrite Elimination by Pd-Based Catalysts using Formic Acid as a Reducing Agent

BELTRAME, T. F; F. M. ZOPPAS; RODRIGUES, M. A. S.; AGHEMO, V. S.; MARCHESINI, F. A.; BERNARDES, A. M.; DA SILVA, S. W.

Paphos

Simposio; 5th Intl. Symp. on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development; 2019

Flogen Star OUTREACH

In recent years, the contamination of drinking water with nitrogen compounds is increasing due to the poor disposal of animal waste and excessive consumption of fertilizer. Nitrates and nitrites present in water produce serious problems for human health. Acceptable limits for nitrate, nitrite, and ammonium in drinking water were set by the World Health Organization at 50 ppm, 3 ppm and 0.5 ppm respectively [1]. The past few years have seen diverse technologies for nitrate and nitrite elimination, such as reverse osmosis, electrodialysis, ion exchange, catalytic abatement and biodenitrification. Among them, for the nitrite case, the catalytic reduction results in attraction due to easy accessibility, low investment costs, no need of additional treatment, and so on. In catalytic technology, a noble metal catalyst is used, like Pd, supported on a different massive oxide (i.e. alumina, silica Si:Al30). H2 (g) is used as reducing agent for promoting the nitrite reduction to gaseous nitrogen. In this sense, formic acid (FA) has been considered as a way to store H2 (g) and it could be used as a reducing agent for nitrite reduction [2]. To the best of our knowledge, there are no studies of catalytic removal of nitrite using formic acid as a reducing agent. Since this agent is suitable for the removal of nitrate, the study of this agent in nitrite removal deserves attention. The objective of this study was to investigate the behavior of formic acid as a hydrogen source in the catalytic reduction of nitrite (100 N-ppm) present in drinking or waste water.Pd catalysts, supported on alumina, silica, and a mixture of Si:Al30, were synthesized by wet impregnation and evaluated for nitrite removal in a batch reactor. Palladium chloride (PdCl2) was used as a precursor.The results obtained show that in the presence of FA and without a catalyst, nitrite was 80% oxidized to nitrate. This reaction follows a chemical equilibrium between these two compounds [3]. In all tests, nitrate formation occurred. On the other side, it was found that using catalysts, the formation of nitrate is lower, in comparison with its formation without a catalyst. The catalyst which shows the best selectivity to N2 in the same conversion rate (95%) was the one supported in alumina (55%). The nitrate selectivities obtained in the same conversion (95%) are 80%, 55%, 45% and 65% for formic acid, PdSi:Al30, alpha-Al2O3, PdSiO2 respectively. Also, in the same order, the ammonium selectivities obtained in the same conversion (95%) are: 0%, 0.9%, 0% and 0%, respectively. Therefore, alpha-Al2O3 promotes a better selectivity to gaseous compounds, making it the most promising support among those evaluated for this reaction. The use of FA shows a promising result, which must be optimized for its future use in catalytic nitrogen removal processes.