Monochloromethane Research Articles

Unveiling the Function of Oxygen Vacancy on Facet-Dependent CeO2 for the Catalytic Destruction of Monochloromethane: Guidance for Industrial Catalyst Design.

Secondary pollution remains a critical challenge for the catalytic destruction of chlorinated volatile organic compounds (CVOCs). By employing experimental studies and theoretical calculations, we provide valuable insights into the catalytic behaviors exhibited by ceria rods, cubes, and octahedra for monochloromethane (MCM) destruction, shedding light on the elementary reactions over facet-dependent CeO2. Our findings demonstrate that CeO2 nanorods with the (110) facet exhibit the best performance in MCM destruction, and the role of vacancies is mainly to form a longer distance (4.63 Å) of frustrated Lewis pairs (FLPs) compared to the stoichiometric surface, thereby enhancing the activation of MCM molecules. Subsequent molecular orbital analysis showed that the adsorption of MCM mainly transferred electrons from the 3σ and 4π* orbitals to the Ce 4f orbitals, and the activation was mainly caused by weakening of the 3σ bonding orbitals. Furthermore, isotopic experiments and theoretical calculations demonstrated that the hydrogen chloride generated is mainly derived from methyl in MCM rather than from water, and the primary function of water is to form excess saturated H on the surface, facilitating the desorption of generated hydrogen chloride.

Design of hydrodechlorination catalysts on the basis of chloromethanes-metallic active sites interactions

The adsorption of chloromethanes, namely trichloromethane (TCM), dichloromethane (DCM) and monochloromethane (MCM), and hydrogen on metal clusters of Pd, Pt, Rh and Ru was studied by molecular simulation to learn on the design of more efficient catalysts for the hydrodechlorination (HDC) of those species. All the above metals showed high dechlorination ability, following in all cases the order TCM > DCM > MCM. The computational study consigns that dissociative adsorption of chloromethanes is promoted on the zero-valent metal (M0) sites while non-dissociative adsorption, associated to catalyst deactivation, is strongly favored on the electro-deficient ones.The dechlorination ability of M0 species follows the order Ru > Rh > Pt > Pd, with greater differences in the dechlorination of TCM. Conversely, hydrogenation ability remarkably decreases from Pd and Pt to Rh and Ru catalysts. This determines a more favorable balance of reactant adsorption energies in the HDC with Pd, especially for TCM HDC. Based on the theoretical findings, catalysts with high proportion of zero-valent metal species, supported on CeO2-Sm2O3 (CS), were prepared, characterized and tested in the HDC of TCM and DCM in lab-scale continuous fixed bed experiments. The conclusions obtained by simulation were supported by the experimental results. The high proportion of zero-valent species in the Pd/CS catalyst, besides the favorable interactions between active sites and both chloromethanes and H2, allow an outstanding performance of the catalyst in the HDC of those chloromethanes, with a significantly higher dechlorination activity and stability than the other metals for the HDC of TCM.

Abatement of dichloromethane with high selectivity over defect-rich MOF-derived Ru/TiO2 catalysts.

The regulation of oxygen vacancies and Ru species using metal-organic frameworks was synergically adopted in a rational design to upgrade Ru/TiO2 catalysts, which are highly active for the catalytic oxidation of dichloromethane (DCM) with less undesired byproducts. In this work, Ru/M-TiO2 and Ru/N-TiO2 catalysts were synthesized by the pyrolysis of MIL-125 and NH2-MIL-125 incorporated with Ru, the existence of Ru nanoclusters and nanoparticles was detected by XAFS, respectively, and the catalytic performance was analyzed comprehensively. Complete oxidation of DCM was obtained at ∼290 °C over Ru/M-TiO2 and Ru/N-TiO2 catalysts, while Ru/N-TiO2 showed quite less monochloromethane (MCM) and higher CO2 yields, and better dechlorination capacity in oxidation. The distinction comes down to that the easier desorption of chlorine could be achieved over Ru4+ which act as the main activated adsorption sites for DCM in Ru/N-TiO2, compared to oxygen vacancies that serve as the main dissociation sites in Ru/M-TiO2. Additionally, Ru/N-TiO2 exhibited superior stability and excellent resilience in moisture. An in situ DRIFTS experiment further indicated the different DCM catalytic degradation process as well as the reaction mechanism over the as-prepared catalysts.

Energy, exergy analysis of conceptually designed monochloromethane production process from hydrochlorination of methanol

In this work, an integrated Exergetic evaluation was proposed to establish a better utilization of energy within the system and to achieve a sustainable environment. A simulation file was brought into being for the Synthesis of Monochloromethane (MCM) from hydrochlorination of methanol process with the ASPEN HYSYS simulator. An explorative analysis on thermodynamic derivatives like Energy and Exergy for the entire process subunits (and/or components) was carried out, which includes the quantity of Energy loss, exergy destruction and exergy efficiency among all process components. From the calculated figures in all of them, the reactor followed by the absorber has maximum exergy destruction of 138 MW and 29 MW respectively. Moreover, an observation found that exergy destruction of 266 MW was engaged with Heat Exchanger Network (HEN) i.e., 47.5 % of total MCM pant destruction. Retrofit design is the possible way to reduce the exergy destruction rate employed with HEN without any interruption to the properties of process streams. This retrofit design confines exergy destruction to 187 MW which is 38.8 % of total process destruction. The total energy, exergy efficiencies are 85.45 % and 93.9 % respectively.

Effect of Ni–V loading on the performance of hollow anatase TiO2 in the catalytic combustion of dichloromethane

A catalyst based on mixed V-Ni oxides supported on TiO2 (Ni–V/TiO2) was obtained using the sol–gel method. Its catalytic performance relative to dichloromethane (DCM) degradation was investigated. Characterization and analysis were conducted using transmission electron microscopy, H2 temperature-programmed reduction, pyridine–Fourier transform infrared spectroscopy (FTIR) characterization, and X-ray diffraction. Results showed that the original hollow anatase structure of pure TiO2 was well-maintained after Ni–V loading. The loading of NiO–VOx not only significantly improved the stability of pure TiO2 but also inhibited the formation of the by-product monochloromethane (MCM). Among the series of Ni–V/TiO2 catalysts, 4%Ni–V/TiO2 possessed the highest catalytic activity, with 90% DCM conversion at only 203°C. No by-products and no significant changes in the catalytic activity were observed during combustion of DCM after 100 hr of a continuous stability test. Furthermore, thermogravimetric analysis (O2-TG) and energy dispersive spectrometer (EDS) characterization of the used 4%Ni–V/TiO2 catalyst revealed that no coke deposition or chlorine species could be detected on the catalyst surface.

Phosphate-Functionalized CeO2 Nanosheets for Efficient Catalytic Oxidation of Dichloromethane.

Tuning the nature and profile of acidic and basic sites on the surface of redox-active metal oxide nanostructures is a promising approach to constructing efficient catalysts for the oxidative removal of chlorinated volatile organic compounds (CVOCs). Herein, using dichloromethane (DCM) oxidation as a model reaction, we report that phosphate (PO x) Brønsted acid sites can be incorporated onto a CeO2 nanosheet (NS) surface via an organophosphate-mediated route, which can effectively enhance the CeO2's catalytic performance by promoting the removal of chlorine poisoning species. From the systematic study of the correlation between PO x composition, surface structure (acid and basic sites), and catalytic properties, we find that the incorporated Brønsted acid sites can also function to decrease the amount of medium-strong basic sites (O2-), reducing the formation of chlorinated organic byproduct monochloromethane (MCM) and leading to the desirable product, HCl. At the optimized P/Ce ratio (0.2), the PO x-CeO2 NSs can perform a stable DCM conversion of 65-70% for over 10 h at 250 °C and over 95% conversion at 300 °C, superior to both pristine and other phosphate-modified CeO2 NSs. Our work clearly identifies the critical role of acid and basic sites over functionalized CeO2 for efficient catalytic CVOCs oxidation, guiding future advanced catalyst design for environmental remediation.

Application of B-=SUB=-12-=/SUB=-N-=SUB=-12-=/SUB=- and B-=SUB=-12-=/SUB=-P-=SUB=-12-=/SUB=- as two fullerene-like semiconductors for adsorption of halomethane: density functional theory study

We examined and discussed the interaction of two halomethanes (mono-chloromethane (MCM), and mono-fluoromethane (MFM) ) with B12N12 and B12P12 fullerene-like semiconductors based on density functional theory (DFT). We calculated adsorption energies and followed the changes in the electronic structure of semiconductors upon adsorption of MCM and MFM. We found that the adsorption on the B12N12 nano-cluster is energetically more favorable compared to B12P12 nano-cluster. Also for both systems we found higher values of adsorption energy for MFM than for MCM. We found that upon adsorption of above-mentioned species on these two fullerene-like semiconductors, the HOMO-LUMO distributions and also the gap energy for each system did not change significantly, which correspond to the physisorption process. As a result, B12N12 is a more appropriate nano-cluster to be used as a selective sensor for halomethanes, especially for MFM. DOI: 10.21883/FTP.2017.01.8191

Application of B12N12 and B12P12 as two fullerene-like semiconductors for adsorption of halomethane: Density functional theory study

We examined and discussed the interaction of two halomethanes (mono-chloromethane (MCM), and mono-fluoromethane (MFM)) with B12N12 and B12P12 fullerene-like nanocages as semiconductor based on density functional theory (DFT). We calculated adsorption energies and followed the changes in the electronic structure of semiconductors upon adsorption of MCM and MFM. We found that the adsorption on the B12N12 nano-cluster is energetically more favorable compared to B12P12 nano-cluster. Also for both systems we found higher values of adsorption energy for MFM than for MCM. We found that upon adsorption of above-mentioned species on these two fullerene-like semiconductors, the HOMO–LUMO distributions and also the gap energy for each system did not change significantly, which correspond to the physisorption process. As a result, B12N12 is a more appropriate nano-cluster to be used as a selective sensor for halomethanes, especially for MFM.

Increased formation of halomethanes during chlorination of chloramphenicol in drinking water by UV irradiation, persulfate oxidation, and combined UV/persulfate pre-treatments

Ultraviolet/persulfate (UV/PS) has been widely used to generate sulfate radicals for degradation of water organic pollutants in previous studies. However, its impacts on disinfection byproduct formation during post-chlorination of degraded compounds is unclear. The objective of this study was to evaluate the impacts of UV irradiation, PS oxidation, and the combined UV/PS advanced oxidation process (AOP) pre-treatments on halomethane formation during the following chlorination of chloramphenicol (CAP), a model antibiotic commonly found in wastewater-impacted water. Results showed that CAP could be transformed to more trichloromethane (TCM) than monochloromethane (MCM) and dichloromethane (DCM) in the presence of excess chlorine. UV photolysis, PS oxidation and UV/PS AOP all directly decomposed CAP to produce halomethanes (HMs) before post-chlorination. Moreover, UV and UV/PS pre-treatments both enhanced the formation of all the HMs in the subsequent chlorination. PS pre-oxidation decreased the TCM formation during post-chlorination, but increased the yields of MCM, DCM and total HMs. UV pre-irradiation significantly increased the bromide utilization of HMs, whereas UV/PS pre-oxidation decreased the bromine incorporation and utilization of HMs from the chlorination of CAP in a low-bromide water. UV irradiation, PS oxidation, and UV/PS AOP can inactivate pathogens and degrade organic pollutants, but this benefit should be weighed against a potential risk of the increased halomethane formation from degraded organic pollutants with and without post-chlorination.