Support induced influence on the reactivity and selectivity of nitrate reduction by Sn-Pd bimetallic catalysts. Issue 3 (June 2020)

• Record Type: Journal Article
• Authors: Hamid, Shanawar; Niaz, Yasir; Bae, Sungjun; Lee, Woojin
• Is Part Of: Journal of environmental chemical engineering. Volume 8:Issue 3(2020)
• Publication Date: 2020-06
• Subjects: Catalytic nitrate reduction -- Kaolinite -- Red mud -- Metal-Support surface interaction -- Bimetallic catalyst; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2020.103754
• Languages: English
• ISSNs: 2213-2929

Abstract

Graphical abstract: Highlights: Sn-Pd-kaolinite showed faster NO3 − reduction kinetics. Sn-Pd-red mud showed higher N2 selectivity. A low Sn:Pd allowed their optimal proximity on the red mud support. Sn-Pd-red mud showed stable kinetics and selectivity over a wide range of CO2 :H2. The reactivity of Sn-Pd-kaolinite was strongly affected by groundwater impurities. Abstract: In this study, two different materials i.e., naturally occurring kaolinite (Al-Si containing structured clay) and industrially produced red mud (mixture of metal oxides) were used as support surfaces for Sn-Pd bimetallic catalysts to investigate the effects of support on catalytic nitrate (NO3 − ) reduction. Under the same experimental conditions, the Sn-Pd-kaolinite reduced NO3 − at a higher rate (k = 15.46 × 10 −2 min −1 ) and lower N2 (70 %) selectivity compared to that of Sn-Pd-red mud, which exhibited slower reduction kinetics (k = 9.16 × 10 −2 min −1 ) but higher N2 selectivity (85 %). We found that support material with a relatively low surface area (i.e., red mud) provided optimal Sn-Pd proximity at relatively low Sn:Pd ratios, but suffered from metallic overlap at high Sn:Pd ratios. Temperature program reduction (TPR) analysis showed that the kaolinite interaction with the Sn-Pd ensembles maintained a higher H2 activation capacity, which resulted in fast reduction kinetics but low N2 selectivity. However, the red mud support exhibited a strong alloying effect toward the Sn-Pd ensembles and regulated the H2 capacity of the Pd to suppress the reduction kinetics and NH4 + selectivity. The NO3 − removal and byproduct selectivity was sustainable over a wide range of CO2 :H2 ratios. Sn-Pd-red mud showed a 100 % NO3 − removal and ∼85 % N2 selectivity at CO2 :H2 ≥ 0.6, while complete NO3 − removal was obtained by Sn-Pd-kaolinite at CO2 :H2 ≥ 1. A groundwater NO3 − removal experiment showed that the reactivity of the Sn-Pd-red mud was stable toward fouling by impurities.