Isotopic evidence (δ13C, δ37Cl, δ2H) for distinct transformation mechanisms of chloroform: Catalyzed H2-water system vs. zero-valent iron (ZVI)

• Published in: Journal of environmental chemical engineering Vol. 11; no. 3; p. 110005
• Main Authors: Asfaw, Berhane Abrha, Sakaguchi-Söder, Kaori, Schiedek, Thomas, Michelsen, Nils, Bernstein, Anat, Siebner, Hagar, Schüth, Christoph
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2023
• Subjects: Catalytic hydrodechlorination; Chloroform; CSIA; Pd/Al2O3; Rh/Al2O3; ZVI; Rh/Al2O3; Catalytic hydrodechlorination; Chloroform; ZVI; Pd/Al2O3; CSIA
• ISSN: 2213-3437
• DOI: 10.1016/j.jece.2023.110005

Catalytic hydrodechlorination is an efficient technology for degrading organochlorinated compounds, such as chloroform (CF), into harmless products. Compound-specific stable isotope analysis (CSIA) of multiple elements is widely used for the investigation of degradation mechanisms. Yet, its application in the study of catalytic hydrodechlorination is still limited. We have applied CSIA to derive chlorine, carbon, and hydrogen isotope enrichment factors (ε) during the degradation of CF over Pd/Al2O3 and over Rh/Al2O3. In addition, the enrichment factors for the same isotopes were derived for the reaction of CF with zero-valent iron (ZVI) for comparison. For the reactions of CF over Pd/Al2O3 and Rh/Al2O3, εC values (−21.9 ± 0.25 ‰ and −23.4 ± 2.3 ‰) and εCl values (−12.1 ± 1.7 ‰ and −10.3 ± 0.6 ‰) were determined, respectively. The corresponding εC and εCl values, for the dechlorination of CF with ZVI were −22.2 ± 2.8 ‰ and −4.7 ± 0.45 ‰, respectively. The apparent kinetic isotope effects (AKIE) of Cl suggest that the transformation mechanism in the catalyzed hydrogen-water system is a non-concerted reaction, unlike the known reductive dechlorination of CF with ZVI. Moreover, dual-isotope slopes (ΛC/Cl) for both catalyzed reactions (ΛPd = 1.8 ± 0.13 and ΛRh = 2.1 ± 0.14) are markedly different than for the ZVI (ΛZVI = 5.8 ± 0.41), reflecting that the reactions proceed in different mechanisms. For hydrogen isotopes, while there was no clear trend for the catalyzed reactions, an inverse secondary hydrogen isotope effect was observed for the reaction of CF with ZVI. •C- and Cl-isotopes of chloroform (CF) fractionated over Pd/Al2O3 and Rh/Al2O3.•Results were compared with dechlorination of CF with zero-valent iron (ZVI).•CF transformation mechanisms for catalyzed reactions are different compared to ZVI.•Inverse secondary H-isotope effect of CF with ZVI was observed.