Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a "bottleneck" for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of MnCeO/HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (E), Brønsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H-TPR, pyridine-IR, DRIFT, and O-TP-Ms. Experimental results revealed that the Brønsted/Lewis (B/L) ratio of MnCeO/HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mn (where the exchange with Ce did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic tetrachloromethane, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, etc.; high humid operational environment could ensure a stable performance for MnCeO/HZSM-5 catalysts; this was due to the effective removal of Cl• and coke accumulations by HO washing, and the distinct increase of Lewis acidity by the interaction of HO with HZSM-5. This work gives an in-depth view into the CB oxidation over acidic solid-supported catalysts and could provide practical guidelines for the rational design of reliable catalysts for industrial applications.

In this article, the underlying eff ect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La3Mn2O7 was explored. Acid treatment led to the formation of LaPO4 and enhanced the mobility of lattice oxygen of La3Mn2O7 evidenced by a range of characterization (i.e., X-ray diff raction, temperature-programmed analyses, NH3−IR, etc.). The former introduced thermally stable Bronsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions (T90 of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.

No abstract

Layered perovskites possess frameworks that can sustain a larger extent of oxygen nonstoichiometry than perovskites, which makes them possibly more suitable for catalytic applications. However, there is little work in literature concerning the catalytic behaviors of them. In this paper, La n+1Ni n O3n+1 layered perovskites were selected as potential catalysts for catalytic oxidation of toluene and methane. The activation and transmission of active oxygen species over the layered structure were explored by using a range of analytical techniques, e.g., O2-TPD, XPS, and H2-TPR. It was noted that the LaNiO3 (n = ∞) that possessed the most chemisorbed oxygen species had the lowest activation energy (E a, ca. 70.1 kJ mol–1) in toluene oxidation and the La4Ni3O10 (n = 3) that owned a superior lattice oxygen mobility showed the lowest E a (ca. 111.0 kJ mol–1) in methane oxidation. The La2NiO4 (n = 1) that lacked chemisorbed and superficial lattice oxygen species yielded the highest E a in either toluene or methane oxidation. It is expected that the work conduct herein could generate more awareness onto the potential catalyst application for layered perovskites and would also give promising insights into the correlation between structural framework and catalytic behaviors for extraordinary materials.