Oxidation Of Vinyl Chloride Research Articles

Viability of strontium carbonate-modified Co3O4 catalysts for chlorinated VOCs oxidation

A series of cobalt oxide catalysts modified with strontium carbonate (Sr:Co molar ratios 0.1–0.4) were prepared, characterised using various techniques (N2 physisorption, XRD, SEM, SEM-EDX, H2-TPR, O2-TPD, XPS) and kinetically evaluated in the gas-phase oxidation of vinyl chloride and 1,2-dichloroethane. Initially, the incorporation of strontium enhanced several physico-chemical properties, including increased surface area, reduced crystal size, and a higher amount of surface oxygen species, suggesting improved catalytic performance. However, the Sr-Co catalysts showed relatively poor catalytic stability, with an increase in chlorinated organic species as catalytic activity decreased. The used catalysts exhibited high concentrations of chlorine, particularly on the surface, along with a decrease in surface area and an increase in crystallite size. Additionally, a reduction in surface oxygen species, crucial for pollutant oxidation, was observed. Therefore, this catalytic chlorination, combined with the loss of textural and structural properties, were inferred to be closely related to catalysts deactivation.

Revealing the effect of framework acidity on the catalytic combustion of vinyl chloride over zeolite-based catalysts

The study explored the effect of different types of acid sites on the catalytic combustion of vinyl chloride over zeolite-based catalysts. MFI-type zeolites were synthesized using impregnation method and loaded with the noble metal Ru. Results indicated that the Ru/Sn-MFI catalysts possessed only Lewis acid sites, the Ru/Al-MFI catalysts were primarily governed by Brønsted acid sites, and the Ru/Si-MFI catalysts had no acid sites. The Ru/Sn-MFI catalyst containing Lewis acid sites demonstrated increased catalytic activity, with a T90 of up to 306 °C, and efficiently prevented the formation of chlorinated by-products. In contrast, the Ru-Si/MFI catalyst exhibited inferior catalytic activity. While a significant amount of chlorinated by-products was generated on the Ru/Al-MFI catalyst. The substantial amount of Lewis acid sites on the surface of Ru/Sn-MFI catalyst facilitated the activation of C-Cl bonds and the cleavage of C–C bonds. Furthermore, the Ru/Sn-MFI catalysts had improved low-temperature reducibility and oxygen mobility, which contributed to the deep oxidation of vinyl chloride.

Hierarchical ZSM-5 zeolite supported RuOx catalysts via organic mesoporous porogens for catalytic oxidation of vinyl chloride

Hierarchical ZSM-5 zeolites supported RuOx catalysts were prepared via the addition of various organic mesoporous porogens (namely starch, cellulose and sucrose) for catalytic oxidation of vinyl chloride (VC). The usage of mesoporous porogens during catalysts preparation was favorable for boosting the catalytic activity of the resultant catalysts, and 1%RuOx/HZ5-10%sucrose exhibited the optimum catalytic activity, impressive catalytic stability and long-term durability. The structure-activity dependence from catalysts characterizations revealed that the higher specific surface area, more abundant strong acid sites and surface adsorbed oxygen species were regarded as the critical parameters for the noticeable improvement of catalytic activity. Based on in situ infrared spectroscopy analysis, 1%RuOx/HZ5-10%sucrose exhibited higher adsorption capacity and more efficient conversion of VC molecules with fewer formation of organic intermediates because of its superior catalytic activity in comparison with the single 1%RuOx/HZ5. Additionally, enol and carboxylate species were demonstrated to be the key organic intermediates in catalytic VC oxidation.

Mn-Zr composite oxides for catalytic vinyl chloride oxidation: The deactivation and mechanism study

Mn-Zr composite oxides for catalytic vinyl chloride oxidation: The deactivation and mechanism study

Co3O4 hollow nanotubes for the catalytic oxidation of C2-chlorinated VOCs

Structured Co3O4 catalysts with a hollow nanotube morphology were prepared by several synthesis routes based on the Kirkendall effect. The resulting samples were kinetically evaluated in the gas-phase oxidation of vinyl chloride and 1,2-dichloroethane, two model C2-chlorinated volatile organic compounds; and exhaustively characterised by means of BET measurements, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry and temperature-programmed techniques (adsorption of ammonia and chlorinated VOC, O2-TPD, H2-TPR and TPO). The performance of the prepared nanotubes was essentially controlled by the presence of active oxygen species at the surface, which in turn depended on the Co2+/Co3+ molar ratio, and the adsorption capacity of the catalyst for the chlorocarbon. Both pollutants were efficiently converted to deep oxidation products at relatively low temperatures. In addition, the optimal catalyst exhibited an appreciable stability when operating during 120 h.

Barium carbonate promoted cobalt oxide as highly efficient catalyst for the total oxidation of vinyl chloride

Co-based catalyst has excellent chlorine resistance, so it is an effective catalyst to degrade VC at present. A series of high-performance CoxBa1 catalysts were prepared by doping Ba into Co3O4 and changing the Ba/Co mol ratio. Under the condition of space velocity of 15,000 ml·g−1·h−1, the conversion rate of VC reached 90% at 199 °C in Co19Ba1, the temperature is much lower than T90 of pure Co3O4 (309 °C), and the catalysis activity of Co19Ba1 was higher than that of the other alkali metal-doped Co19M1 (M = Sr, Ca). Ba species in CoxBa1 mainly exist in the form of BaCO3. With the addition of BaCO3, the particle size of CoxBa1 decreases, resulting in the increase of active site of CoxBa1. BaCO3 can also make CoxBa1 obtain better low-temperature reducibility and more active components. In addition, the increase of BaCO3 content will also increase the basic sites of CoxBa1, and more basic sites can effectively protect Co3O4 from Cl poisoning. When Ba/Co is 1/19, the content of BaCO3 is the highest, so Co19Ba1 also shows the best activity.

Mn–Zr composite oxides as efficient catalysts for catalytic oxidation of vinyl chloride

Mn–Zr composite oxides with variable molar ratios of Mn/Zr were prepared by a citrate sol–gel method for catalytic oxidation of vinyl chloride. The structure–activity relationship was studied by numerous characterization and experimental approaches.

Catalytic oxidation of vinyl chloride over Co–Ce composite oxides derived from ZIF-67 template: Effect of cerium incorporation

Transition metal oxides are regarded as an economical and efficient catalytic alternate for catalytic oxidation of volatile organic compounds (VOCs) emissions. The morphological decoration and the incorporation of extrinsic metals were demonstrated to be effective strategies for achieving noticeable catalytic improvement. In this work, a novel Co–Ce composite oxides catalyst was obtained by the pyrolysis of ZIF-67 template with the impregnation of certain cerium cations (denoted as ZIF-CoCe). Compared with the reference Co–Ce composite oxides by the sol-gel (denoted as SG-CoCe) and physical mixing (denoted as MIX-CoCe) methods, ZIF-CoCe delivers significantly higher catalytic activity for vinyl chloride oxidation, which are demonstrated to be closely related with its superior redox capacity, more abundance of surface active Co3+ sites and adsorbed active oxygen species from oxygen vacancies. In addition, the unique cage-like morphological feature of the Co-based catalysts derived from ZIF-67 template plays a crucial function in kinetically facilitating the mass transfer of catalytic reaction and promoting the catalytic VC oxidation activity. With regard to in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analysis, enol and carboxylic acid species are identified to be the key organic intermediates during catalytic vinyl chloride oxidation.

Micro-meso hierarchical ZSM-5 zeolite supported RuOx nanoparticles for activity enhancement of catalytic vinyl chloride oxidation

Hierarchical ZSM-5 zeolites were synthesized by an alkali hydrothermal treatment strategy and adopted as support materials for the fabrication of RuOx nano catalysts. The physicochemical properties and catalytic activities for vinyl chloride (VC) oxidation over the resultant RuOx/HZ5-nd (n = 2, 3, 4) catalysts were successfully modulated by the treatment time regulation (2d, 3d and 4d) of ZSM-5 solid. Experimental results demonstrated that the RuOx/HZ5-nd catalysts possessed notable cavity-shell structures with micro-meso hierarchical porosity, which brought about the increased specific surface area, the enhanced low-temperature reducibility and the strengthened surface acidity comparable to RuOx/HZ5. All these superiorities were recognized as the crucial origin for boosting catalytic oxidation of VC. Especially, the RuOx@HZ5-3d catalyst exhibited the optimum VC oxidation activity with the lowest T50 and T90 (temperature at 50 and 90% conversion) of 275 and 297 °C, which was 22 and 24 °C lower than those of RuOx/HZ5. Importantly, RuOx@HZ5-3d exhibited significantly high thermal stability, water resistant and regeneration capacity from humid conditions, which made it a promising material for the catalytic purification of chlorinated volatile organic compounds.

Contrasting regulatory effects of organic acids on aerobic vinyl chloride biodegradation in etheneotrophs.

Vinyl chloride (VC) is a common groundwater pollutant generated during anaerobic biodegradation of chlorinated solvents (e.g., trichloroethene (TCE) or tetrachloroethene (PCE)). Aerobic VC biodegradation by etheneotrophs can support anaerobic PCE and TCE bioremediation to achieve complete removal in situ. However, anaerobic bioremediation strategies necessitate biostimulation with electron donors that are fermented in situ, generating organic acids that could influence aerobic VC biodegradation processes. We examined the effect of organic acids (lactate, acetate, propionate, and butyrate) on aerobic VC biodegradation by VC-assimilating etheneotrophs Mycobacterium strain JS60 and Nocardioides strain JS614. Strain JS60 grew on all organic acids tested, while strain JS614 did not respond to lactate. VC-grown strain JS60 fed VC and one or more organic acids showed carbon catabolite repression (CCR) behavior where VC biodegradation occurred only after organic acids were depleted. In contrast, CCR was not evident in VC-grown strain JS614, which degraded VC and organic acids simultaneously. Acetate-grown JS60 showed similar CCR behavior when fed VC and a single organic acid, except that extended lag periods (5-12days) occurred before VC oxidation ensued. Acetate-grown JS614 fed VC and either acetate or butyrate displayed 5-8day lag periods before simultaneous VC and organic acid biodegradation. In contrast, acetate-grown JS614 degraded VC and propionate without a significant lag, suggesting a regulatory link between propionate and VC oxidation in JS614. Different global regulatory mechanisms controlling VC biodegradation in the presence of organic acids in etheneotrophs have implications for developing combined anaerobic-aerobic bioremediation strategies at chlorinated ethene-contaminated sites. KEY POINTS: • With organic acids present, VC utilization was repressed in JS60, but not in JS614 • Strain JS60 grew readily on lactate, while strain JS614 did not • Propionate alleviated lag periods for VC utilization in acetate-grown JS614.

Effectiveness of Permeable Reactive Bio-Barriers for Bioremediation of an Organohalide-Polluted Aquifer by Natural-Occurring Microbial Community

In this study, a bioremediation approach was evaluated for the decontamination of an aquifer affected by the release of organohalides by an industrial landfill. After preliminary physicochemical and microbiological characterization of the landfill groundwater, the stimulation of natural organohalide respiration by the addition of a reducing substrate (i.e., molasse) was tested both at microcosm and at field scales, by the placement of an anaerobic permeable reactive bio-barrier. Illumina sequencing of cDNA 16S rRNA gene revealed that organohalide-respiring bacteria of genera Geobacter, Sulfurospirillum, Dehalococcoides, Clostridium and Shewanella were present within the aquifer microbial community, along with fermentative Firmicutes and Parvarchaeota. Microcosm experiments confirmed the presence of an active natural attenuation, which was boosted by the addition of the reducing substrate. Field tests showed that the bio-barrier decreased the concentration of chloroethenes at a rate of 23.74 kg d−1. Monitoring of organohalide respiration biomarkers by qPCR and Illumina sequencing revealed that native microbial populations were involved in the dechlorination process, although their specific role still needs to be clarified. The accumulation of lower-chloroethenes suggested the need of future improvement of the present approach by supporting bacterial vinyl-chloride oxidation, to achieve a complete degradation of chloroethenes.

Insight into the Surface-Tuned Activity and Cl2/HCl Selectivity in the Catalytic Oxidation of Vinyl Chloride over Co3O4(110) versus (001): A DFT Study

Co3O4 has received tremendous attention in the oxidation of chlorinated volatile organic compounds (CVOCs) for its general catalytic oxidation ability. However, to rationally optimize the Co3O4-based catalysts, ascertaining the reaction mechanism and active-site-specific activity variation at the molecular level remains an open issue. Herein, we performed the first-principles calculations to systematically explore the catalytic oxidation process of vinyl chloride (VC) on two representative (110) and (001) surfaces of Co3O4. The reaction pathways of VC oxidation are thoroughly calculated, mainly consisting of three subprocesses, namely, the C–Cl bond scission, CH2CH oxidation, and the elimination of Cl species. Results show that the oxygen vacancy is indispensable to break the C–Cl bond on Co3O4(110), whereas the C–Cl bond cleavage can be achieved by the collaboration of two adjacent Co5c sites at a lower barrier on Co3O4(001). Both surfaces are reactive for the oxidation of the CH2CH group, indicative of the excellent oxidative ability of the Co3O4 catalyst. More importantly, we identify the rate-determining step in the overall VC oxidation as the elimination of Cl species, and HCl is the preferential chlorine-containing product rather than Cl2. In comparison with Co3O4(110), the Co3O4(001) surface gives a lower energy barrier for Cl elimination and indicates its potentially superior performance for VC oxidation. Finally, some propositions are made for how to improve the VC oxidation on Co3O4 catalysts. These fundamental insights identified in this work may provide a theoretical basis for the design and synthesis of Co3O4-based catalysts in CVOC oxidation.

Significant Improvement of Catalytic Performance for Chlorinated Volatile Organic Compound Oxidation over RuOx Supported on Acid-Etched Co3O4

Ru catalysts have attracted increasing attention in catalytic oxidation of chlorinated volatile organic compounds (CVOCs). However, the development of Ru catalysts with high activity and thermal stability for CVOC oxidation still poses significant challenges due to their restrictive relationship. Herein, a strategy for constructing surface defects on Co3O4 support by acid etching was utilized to strengthen the interaction between active RuOx species and the Co3O4 support. Consequently, both the dispersity and thermal stability of RuOx species were significantly improved, achieving both high activity and stability of Ru catalysts for CVOC oxidation. The optimized Ru catalyst on the HF-etched Co3O4 support (Ru/Co3O4-F) achieved complete oxidation of vinyl chloride at 260 °C under 30 000 mL·g-1·h-1, which was lower than 300 °C for the Ru catalyst on the original Co3O4 (Ru/Co3O4). More importantly, the Ru species on the Ru/Co3O4-F catalyst were hardly lost after calcination at 500-700 °C and even reacting at 650 °C for 120 h. On this basis, the polychlorinated byproducts over the Ru/Co3O4-F catalyst were almost completely effaced by phosphate modification on the catalyst surface. These findings show that the method combining acid etching of the support and phosphate modification provides a strategy for the advancement of catalyst design for CVOC oxidation.

Catalytic oxidation of chlorinated volatile organic compounds over Mn-Ti composite oxides catalysts: Elucidating the influence of surface acidity

A series of Mn-Ti composite oxides (MnyTi1−yOx) were prepared via the sol-gel method, and their reducibility and surface acidity were controlled by adjusting the Mn/Ti molar ratio. In addition, as a model reaction, the catalytic activity of Mn-Ti composite oxides for the deep oxidation of vinyl chloride (VC) was evaluated. It was found that the catalyst surface acidity played a decisive role in the oxidation of VC, on the condition that the catalyst reducibility was superior to that of Mn0.4Ti0.6Ox. Consequently, a linear relationship between the surface acidity of the MnyTi1−yOx catalysts (y≥0.4) and the reaction rate of the VC oxidation process was observed. Moreover, the influence of Lewis acidic sites originating from Ti species on the catalytic activity of the MnyTi1−yOx catalysts was revealed. These results could lead to an efficient strategy for enhancing the CVOC oxidation reaction through finely tuning reducibility and surface acidity of the catalyst.

Novel synthetic route to Ce-Cu-W-O microspheres for efficient catalytic oxidation of vinyl chloride emissions

The solubility of ammonium tungstate in a special hydrothermal condition is exploited to synthesize uniform microspheres of Ce-Cu-W-O oxides. Compared to their W-undoped counterparts, they possess more Ce3+ and oxygen vacancies, thereby promoting oxygen mobility. The formed rich WO3 surface can effectively provide acid sites, which is helpful for adsorption of vinyl chloride and interrupting the C–Cl bond. In addition, the presence of WO3 induces the formation of finer CuO nanoparticles with respect to the traditional coprecipitation method, thereby resulting in a better reducibility. Benefiting from both the enhanced acidity and reducibility, the Ce-Cu-W-O microspheres deliver excellent low-temperature vinyl chloride oxidation activity (a reaction rate of 2.01 × 10−7 mol/(gcat·s) at 250 °C) and high HCl selectivity. Moreover, subtle deactivation occurs after the three cycling activity tests, and a stable vinyl chloride conversion as well as mineralization are observed during the 72-h durability test at 300 °C, which demonstrates good thermal stability. Our strategy can provide new insights into the design and synthesis of metal oxides for catalytic oxidation of chlorinated volatile organic compounds.

Ruthenium/cobalt binary oxides supported on hollow alumina microspheres as highly efficient catalyst for vinyl chloride oxidation

Alumina hollow microspheres (Al2O3-hms) were synthesized and used to support metal oxide and binary metal oxide particles to prepare three catalysts, designated as RuOx/Al2O3-hms, CoOx/Al2O3-hms and RuCoOx/Al2O3-hms. Their catalytic properties in vinyl chloride oxidation were investigated and found to follow this order: RuCoOx/Al2O3-hms > RuOx/Al2O3-hms > CoOx/Al2O3-hms. In comparison with a commercial Al2O3 support, the Al2O3-hms provide a higher specific surface area and unique hollow spherical morphology, benefiting for uniform distribution of catalyst particles. It was also found that the strong metal-support interaction between metal nanoparticles and Al2O3-hms has significant effects on the low-temperature reducibility, the surface oxygen abundance and mobility, giving rise to different oxidation activities. The Al2O3-hms supported metal catalysts remained relatively high catalytic activity after consecutive catalytic runs and high-temperature annealing. The anti-sintering ability enhancement of metal particles was attributed to the stabilization and metal-support interaction effects with Al2O3-hms.

An efficient SnyMn1-yOx composite oxide catalyst for catalytic combustion of vinyl chloride emissions

A series of SnyMn1-yOx composite oxide catalysts with different Sn/Mn molar ratios (y = 1.0, 0.8, 0.6, 0.3 and 0) were prepared by a co-precipitation method. The catalysts were investigated for the catalytic combustion of vinyl chloride (VC), which is a typical chlorinated volatile organic compound (CVOC). It is found that the existence of Sn-Mn-O solid solution structure over SnyMn1-yOx catalysts can increase the specific surface area and tune the valence state of Mn and the surface properties. As a result, the redox property and the ability of adsorbing oxygen species of SnyMn1-yOx catalysts are enhanced. Meanwhile, more weak and medium acid sites are present on the catalyst surface. Under the synergetic effects of these above-mentioned factors, the catalytic activity of SnyMn1-yOx catalyst for VC oxidation is significantly improved compared with pure SnOx and MnOx catalysts. Moreover, the Sn/Mn molar ratio significantly affects the catalytic activity of SnyMn1-yOx catalysts, among which Sn0.6Mn0.4Ox catalyst possesses the best catalytic activity and excellent resistance to Cl poisoning and water-resisting ability. It can retain VC conversion of 100% without any chlorinated byproducts for 100 h at the reaction temperature of 340 °C.

Insights into the Morphological Effect of Co3O4 Crystallite on Catalytic Oxidation of Vinyl Chloride

Co3O4 catalysts of cube and sphere shapes were prepared by one-step hydrothermal synthesis with different controlled amounts of Co(NO3)2·6H2O and NaOH. The morphological effects on both physicochemical properties and catalytic activities of vinyl chloride oxidation were investigated by material characterization and performance evaluation. The obtained results showed that the morphology, resulting in the exposure difference of crystal planes, significantly affected the catalytic property. The catalytic activity for vinyl chloride oxidation followed a descending order of Co3O4 cube (Co3O4-c) > Co3O4 sphere (Co3O4-s) > Co3O4 commercial (Co3O4-com). The cube-shaped Co3O4 presented higher catalytic activity and stability than Co3O4 spheres despite their similar crystallographic structures as well as physicochemical and redox properties. Accordingly, the different catalytic behaviors should be attributed to a morphological effect. The Co3O4 cube with a preferential exposure of (001) plane presented higher abundance of surface Co2+ cations and adsorbed oxygen species, which acted as the active sites responsible for the improvement of its catalytic activity.

Catalytic oxidation of low concentrations of vinyl chloride over spinel-type Co3O4 catalysts

In this study, a series of spinel-type Co3O4 catalysts were synthesized by different routes, including template (Co3O4-TP), sol–gel (Co3O4-SG), and precipitation method (Co3O4-CP), and their performance in the catalytic oxidation of vinyl chloride (VC) was investigated. The relationships between the catalysts’ physicochemical properties and performance in the catalytic oxidation of VC were investigated by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, ammonia temperature-programmed desorption, oxygen temperature-programmed desorption and X-ray photoelectron spectroscopy. The results showed that the catalytic activity of the catalysts decreased in the order Co3O4-TP > Co3O4-CP > Co3O4-SG, which was in a good agreement with the trends for the content of acid sites and oxygen vacancies. Notably, the Co3O4-TP catalyst showed the highest catalytic activity towards VC due to its low-temperature reducibility, larger number of adsorbed oxygen species, and higher oxygen mobility. Moreover, it was found that surface-adsorbed oxygen species were essential in the catalytic oxidation of VC. The VC conversion rate over Co3O4-TP calcined at 400 °C achieved 98% at 275 °C, with selectivities towards CO2 and HCl of 95.6 and 80.5%, respectively. In addition, only traces of chlorinated by-products were formed, and the conversion rate of low-concentration VC exceeded 96% after 60 h continuous reaction.

Ruthenium oxides supported on heterostructured CoPO-MCF materials for catalytic oxidation of vinyl chloride emissions

A novel heterostructured material, cobalt phosphate-SiO2 mesostructured cellular foams (CoPO-MCF), was successfully synthesized by in situ growth. The material was characterized by X-ray diffraction (XRD), nitrogen sorption, temperature-programmed reduction (H2-TPR and CO-TPR), temperature-programmed desorption of NH3 (NH3-TPD), and X-ray photoelectron spectroscopy (XPS). A ruthenium precursor was readily introduced and highly dispersed on the CoPO nanophases of the CoPO-MCF through an impregnation method. The resulting Ru/CoPO-MCF catalyst exhibited high catalytic activity for the oxidation of vinyl chloride (VC). The results of three consecutive runs and long-term tests showed high stability of the Ru/CoPO-MCF for the catalytic oxidation of VC. The unique heterostructures of the CoPO-MCF not only improve the reducibility and acidity of the MCF but also strengthen the interaction between ruthenium oxide nanoparticles and the CoPO-MCF support, which contributes to the enhanced catalytic performance.