On the Mechanism of Catalytic Oxidation of CH₂Cl₂ on γ-Al₂O₃ and its Oscillatory Behaviour

Comparative Studies of Phosphate-Modified CeO2 and Al2O3 for Mechanistic Understanding of Dichloromethane Oxidation and Chloromethane Formation

“…Considering the high selectivity of MCM over P-Al 2 O 3 -0.2 and the reported results about Al 2 O 3 -based catalysts, , we considered that there were two possible reasons to explain the low selectivity of MCM over CeO 2 -based catalysts: (1) the formation of MCM was difficult due to the deficiency of the required active sites and (2) the formed MCM could be reoxidized easily. Hereinafter, we focused and comparatively studied CeO 2 - and Al 2 O 3 -based catalysts to further understand the formation of MCM, especially for the roles of redox and basicity sites.…”

“…Haber et al studied the decomposition behavior of DCM on γ-Al 2 O 3 using IR spectroscopy and proposed that MCM was formed through a reaction between the hydride existing on alumina (H − from a hydroxyl group) and adsorbed DCM molecules. 21 and formate species; however, the formation of MCM was not explained. 15 Maupin et al found that MCM would be generated even over Pt/Al 2 O 3 , and this might be ascribed to the disproportionation of DCM.…”

“…Catalytic oxidation of DCM as a typical CVOC was widely studied due to its simple molecular structure, massive emission, and difficulty in being degraded; moreover, the formation of highly selective MCM has been discussed but is still debatable. Haber et al studied the decomposition behavior of DCM on γ-Al 2 O 3 using IR spectroscopy and proposed that MCM was formed through a reaction between the hydride existing on alumina (H – from a hydroxyl group) and adsorbed DCM molecules . van den Brink et al considered that DCM transformed into formaldehyde through the surface hydroxyl groups on γ-Al 2 O 3 and then disproportionated into methoxy and formate species; however, the formation of MCM was not explained .…”

“…Our previous studies indicated that pristine CeO 2 was superiorly active for catalytic combustion of DCM and the selectivity of MCM was almost negligible. However, after anchoring phosphate on CeO 2 , the formation of MCM was apparently accelerated and the maximum selectivity reached about 4% , but was still much less than that of Al 2 O 3 -based catalysts. , The controllability of MCM generation on CeO 2 based catalysts and the significant differences with Al 2 O 3 -based catalysts were regarded as an ideal chance to understand the formation mechanism of MCM during catalytic combustion of DCM. Herein, mechanisms of DCM oxidation and MCM formation over phosphate-functionalized CeO 2 were investigated through a series of well-designed experiments such as isotopic in situ DRIFTS; the pulse reaction of deuterated dichloromethane (DDCM); the application of additional hydrogen donors such as methanol, formaldehyde, and formate; and hydrogen transfer via deuterated methanol (methanol- d 1 and d 3 ).…”

8 Catalysis

“…To account for the second order with respect to the concentration of the acidic sites observed at low-temperature cracking, a new scheme (Scheme 2) involving two Si^O^Al sites is proposed: g-Al 2 O 3 itself has recently been found to be active in the decomposition of CH 2 Cl 2 to CO and HCl with the formation, however, of undesirable CH 3 Cl. 273,274 Haber et al 274 have shown that the deposition of Na on g-Al 2 O 3 leads to a suppression of CH 3 Cl formation, instead Cl 2 appears in the reaction products. The mechanisms of the selective and non-selective pathways have been discussed based on IR studies.…”