Understanding Hydrodechlorination of Chloromethanes. Past and Future of the Technology

Abstract

Chloromethanes are a group of volatile organic compounds that are harmful to the environment and human health. Abundant studies have verified that hydrodechlorination might be an effective treatment to remove these chlorinated pollutants. The most outstanding advantages of this technique are the moderate operating conditions used and the possibility of obtaining less hazardous valuable products. This review presents a global analysis of experimental and theoretical studies regarding the hydrodechlorination of chloromethanes. The catalysts used and their synthesis methods are summarized. Their physicochemical properties are analyzed in order to deeply understand their influence on the catalytic performance. Moreover, the main causes of the catalyst deactivation are explained, and prevention and regeneration methods are suggested. The reaction systems used and the effect of the operating conditions on the catalytic activity are also analyzed. Besides, the mechanisms and kinetics of the process at the atomic level are reviewed. Finally, a new perspective for the upgrading of chloromethanes, via hydrodechlorination, to valuable hydrocarbons for industry, such as light olefins, is discussed.

Black Gold-Based “Antenna–Reactor” To Activate Non-Plasmonic Nickel: Photocatalytic Hydrodechlorination and Hydrogenation Reactions

“…Raman analysis of the used catalyst indicates no carbon or coke formation after the reaction (Figure S14). The conventional catalytic system reported for this DCM to methane reaction needed far harsh reaction conditions (e.g., ∼400 °C), with 70−80% selectivity toward methane, 36 whereas black Au catalyzed this reaction at lower temperature with 100% selectivity toward methane.…”

Catalytic dechlorination of 1,2-DCA in nano Cu0-borohydride system: effects of Cu0/Cun+ ratio, surface poisoning, and regeneration of Cu0 sites

“…The proposed mechanism for cVOCs catalytic reduction implies that the catalyst activates H 2 , chemisorbed on its surface, into a robust reductant (H * ) which then reduces the cVOC molecules dissociatively adsorbed on adjacent sites (Eqs. 1 – 2 ) 10 , 16 , 18 . …”

“…Palladium (Pd) catalysts have already been tested for catalytic reduction of contaminants for both in situ and ex situ field-scale applications 29 , 30 , however, Pd is an expensive metal. Moreover, Pd catalysts can undergo complete and permanent deactivation due to surface poisoning and may not be fully regenerated 14 , 18 . Thus, development of a cost-effective technology capable of degrading recalcitrant cVOCs like 1,2-DCA in aqueous phase, by utilizing a cheaper catalyst such as nano zerovalent copper (nCu 0 ) 14 , 16 , 17 , is an important breakthrough.…”

“…in the outer layer 11 , 31 , 32 . Oxidation state of active sites is very critical for catalyst performance, where both the zerovalent (M 0 ) as well as the electron-deficient (M n+ ) sites would play an important role during hydrodechlorination 18 . Washing step can change the ratio (M 0 /M n+ ) of these sites, which would influence the contaminant degradation efficiency 11 , 31 .…”

“…In the field, groundwater constituents (e.g., anions, humic acids) may alter the surface chemistry of remediant metal by surface poisoning and, consequently, affect its contaminant degradation efficiency 18 , 29 , 30 , 33 – 36 . Past studies reported that Cu was deactivated in the presence of chlorine and sulfur compounds during catalytic dechlorination of gas-phase cVOCs 33 , 35 , 36 .…”