Enhanced Activity and Selectivity of Carbon Nanofiber Supported Pd Catalysts for Nitrite Reduction

Abstract

Pd-based catalyst treatment represents an emerging technology that shows promise to remove nitrate and nitrite from drinking water. In this work we use vapor-grown carbon nanofiber (CNF) supports in order to explore the effects of Pd nanoparticle size and interior versus exterior loading on nitrite reduction activity and selectivity (i.e., dinitrogen over ammonia production). Results show that nitrite reduction activity increases by 3.1-fold and selectivity decreases by 8.0-fold, with decreasing Pd nanoparticle size from 1.4 to 9.6 nm. Both activity and selectivity are not significantly influenced by Pd interior versus exterior CNF loading. Consequently, turnover frequencies (TOFs) among all CNF catalysts are similar, suggesting nitrite reduction is not sensitive to Pd location on CNFs nor Pd structure. CNF-based catalysts compare favorably to conventional Pd catalysts (i.e., Pd on activated carbon or alumina) with respect to nitrite reduction activity and selectivity, and they maintain activity over multiple reduction cycles. Hence, our results suggest new insights that an optimum Pd nanoparticle size on CNFs balances faster kinetics with lower ammonia production, that catalysts can be tailored at the nanoscale to improve catalytic performance for nitrite, and that CNFs hold promise as highly effective catalyst supports in drinking water treatment.

Synthesis of Superparamagnetic Core–Shell Structure Supported Pd Nanocatalysts for Catalytic Nitrite Reduction with Enhanced Activity, No Detection of Undesirable Product of Ammonium, and Easy Magnetic Separation Capability

“…Actually, even with a much larger thickness at ~ 50 nm, Fe signal could still be detected by XPS on Previous studies had demonstrated that the reduction of mass transport limitation could also enhance the catalytic nitrite reduction activity and reduce the product selectivity to NH 4 + . 26,51 For example, D'Arino et al reported ܵ ேு ర శ could be depressed to 1.28% by the use of catalyst support with very low specific surface area and very few pore volume, 26 the reaction to bulk solution from its surface easily, and depressed pH gradient along pores effectively. All these characteristics of the Fe 3 O 4 @SiO 2 /Pd catalyst also contributed to its demonstrated high catalytic nitrite reduction activity without the detection of NH 4 + produced.…”

“…The material characterization results and the catalytic nitrite reduction performances of Fe 3 O 4 @SiO 2 /Pd catalysts with ~ 1%, 2.5%, and 5% Pd nanoparticle contents, respectively.Previous studies suggested that the N 2 selectivity was structure sensitive, and the selectivity to N 2 was enhanced with the increase of Pd nanoparticle size 12,51,55. Smaller Pd nanoparticles had more edges and corners, at which it was probably favorable for nitrite to undergo the deep hydrogenation to NH 4 + , while larger Pd nanoparticles had more flat terraces than smaller one and N 2 would be favorably formed on these sites due to their mild hydrogenation capability.21 In this study, however, no NH 4 + production was detected for all these Fe 3 O 4 @SiO 2 /Pd catalysts, although their Pd nanoparticle size and content were different.…”

Solar Light Photocatalytic Degradation of Nitrite in Aqueous Solution Over CdS Embedded on Metal–Organic Frameworks

“…Nitrite concentrations after photocatalysis were measured by diazotization with sulfanilamide and coupling with N-(1-naphthyl)ethylene diamine (Korgel and Monbouquette 1997). Ammonia was measured by the salicylate method (Shuai et al 2012). UV absorbance was determined by a 722 UV-Vis spectrophotometer.…”

Pd-catalytic hydrodechlorination of chlorinated hydrocarbons in groundwater using H2 produced by a dual-anode system

“…Pd-catalytic reductive hydrodechlorination shows a promise for the remediation of CHCs, offering many advantages over other processes such as quick reaction, no halogenated intermediates and applicability for a broad range of reducible compounds (Agarwal et al, 2007;Knitt et al, 2007;Munakata and Reinhard, 2002;Shuai et al, 2012). Although it has been tested extensively in lab (Choe et al, 2010;Janiak and Okal, 2009;Zhu and Lim, 2007), large-scale treatments in the field are still limited because of the challenges such as H 2 supply and catalyst fouling (Chaplin et al, 2012b;Kopinke et al, 2004).…”