Revealing the intrinsic nature of Ni-, Mn-, and Y-doped CeO2 catalysts with positive, additive, and negative effects on CO oxidation using operando DRIFTS-MS.

The catalytic activity of a transition metal (host) oxide can be influenced by doping with a second cation (dopant), but the key factors dominating the activity of the doped catalyst are still controversial. Herein, CeO2 doped with Ni, Mn, and Y catalysts prepared using aerosol pyrolysis were used to demonstrate the positive, negative, and additive effects on CO oxidation as a model reaction. Various characterization results indicated that Ni, Mn, and Y had been successfully doped into the CeO2 lattice. The catalytic activities of each catalyst for CO conversion were in the order of Ni-CeO2 > Mn-CeO2 > CeO2 > Y-CeO2. Operando DRIFTS-MS and various characterization methods were applied to reveal the intrinsic nature of the doping effects. The accumulation rate of the surface bidentate carbonates determined the CO oxidation. A definition to evaluate the doping effect was proposed, which is anticipated to be useful for developing a rational catalyst with a high CO oxidation activity. The CO oxidation reactivities displayed strong correlations with the surface factors obtained from operando DRIFTS-MS analysis and the structure factors from XPS and Raman analyses.

Insight into the Metal-Support Interaction of Pt and ß-MnO2 in CO Oxidation.

Pt-based catalysts exhibit unique catalytic properties in many chemical reactions. In particular, metal-support interactions (MSI) greatly improve catalytic activity. However, the current MSI mechanism between platinum (Pt) and the support is not clear enough. In this paper, the interaction of 1 wt% Pt nanoparticles (NPs) on ß-MnO2 in carbon monoxide (CO) oxidation was studied. The Pt on ß-MnO2 inhibited CO oxidation below 210 °C but promoted it above 210 °C. A Pt/ß-MnO2 catalyst contains more Pt4+ and less Pt2+. The results of operando DRIFTS-MS show that surface-terminal-type oxygen (M=O) plays an important role in CO oxidation. When the temperature was below 210 °C, Mn=O consumption on Pt/ß-MnO2 was less than ß-MnO2 due to Pt4+ inhibition on CO oxidation. When the temperature was above 210 °C, Pt4+ was reduced to Pt2+, and Mn=O consumption due to CO oxidation was greater than ß-MnO2. The interaction of Pt and ß-MnO2 is proposed.

Unveiling the Surface Chemical Reactions during Multi-Phase Catalytic Oxidation of Soot on Nanoengineering/Interfacing/Doping-Prepared Mn-CeO2 Catalysts Using TG-MS and Operando DRIFTS-MS.

The aerosol pyrolysis method from nitrate precursors was used to prepare the Mn-CeO2 catalyst containing Mn2O3, CeO2, and Mn-doped CeO2 nanoparticles for catalyzing carbonous soot oxidation. The prepared Mn-CeO2 catalysts have high specific surface areas, Ce3+ ratio, and oxygen vacancy defects; these are a benefit for soot oxidation. The T50 for soot oxidation on the 0.57Mn-CeO2 catalyst is as low as 355 °C, which is 329 °C lower than that for soot oxidation without a catalyst. The catalysts were characterized using XRD, SEM-EDS, HRTEM, XPS, Raman spectroscopy, H2-TPR-MS, O2-TPD-MS, soot-TPR-MS, and operando DRIFTS-MS. The functions of Mn2O3, CeO2, and Mn-doped CeO2 in the 0.57Mn-CeO2 catalyst are unveiled. Mn-doped CeO2 plays a key role and CeO2 participates in soot oxidation, while Mn2O3 is used to enhance higher ratios of Ce3+, via the reaction of Mn3+ + Ce4+ = Mn4+ + Ce3+. The mechanism of soot oxidation on Mn-CeO2 was proposed.

DRIFTS-MS Investigation of Low-Temperature CO Oxidation on Cu-Doped Manganese Oxide Prepared Using Nitrate Aerosol Decomposition.

Cu-doped manganese oxide (Cu-Mn2O4) prepared using aerosol decomposition was used as a CO oxidation catalyst. Cu was successfully doped into Mn2O4 due to their nitrate precursors having closed thermal decomposition properties, which ensured the atomic ratio of Cu/(Cu + Mn) in Cu-Mn2O4 close to that in their nitrate precursors. The 0.5Cu-Mn2O4 catalyst of 0.48 Cu/(Cu + Mn) atomic ratio had the best CO oxidation performance, with T50 and T90 as low as 48 and 69 °C, respectively. The 0.5Cu-Mn2O4 catalyst also had (1) a hollow sphere morphology, where the sphere wall was composed of a large number of nanospheres (about 10 nm), (2) the largest specific surface area and defects on the interfacing of the nanospheres, and (3) the highest Mn3+, Cu+, and Oads ratios, which facilitated oxygen vacancy formation, CO adsorption, and CO oxidation, respectively, yielding a synergetic effect on CO oxidation. DRIFTS-MS analysis results showed that terminal-type oxygen (M=O) and bridge-type oxygen (M-O-M) on 0.5Cu-Mn2O4 were reactive at a low temperature, resulting in-good low-temperature CO oxidation performance. Water could adsorb on 0.5Cu-Mn2O4 and inhibited M=O and M-O-M reaction with CO. Water could not inhibit O2 decomposition to M=O and M-O-M. The 0.5Cu-Mn2O4 catalyst had excellent water resistance at 150 °C, at which the influence of water (up to 5%) on CO oxidation could be completely eliminated.

Mechanistic Insight into Catalytic Combustion of Ethyl Acetate on Modified CeO2 Nanobelts: Hydrolysis-Oxidation Process and Shielding Effect of Acetates/Alcoholates.

In this study, based on the comparison of two counterparts [Mn- and Cr-modified CeO2 nanobelts (NBs)] with the opposite effects, some novel mechanistic insights into the ethyl acetate (EA) catalytic combustion over CeO2-based catalysts were proposed. The results demonstrated that EA catalytic combustion consisted of three primary processes: EA hydrolysis (C-O bond breakage), the oxidation of intermediate products, and the removal of surface acetates/alcoholates. Rapid EA hydrolysis typically occurs on surface acid/base sites or hydroxyl groups, and the removal of surface acetates/alcoholates resulting from EA hydrolysis is considered the rate-determining step. The deposited acetates/alcoholates like a shield covered the active sites (such as surface oxygen vacancies), and the enhanced mobility of the surface lattice oxygen as an oxidizing agent played a vital role in breaking through the shield and promoting the further hydrolysis-oxidation process. The Cr modification impeded the release of surface-activated lattice oxygen from the CeO2 NBs and induced the accumulation of acetates/alcoholates at a higher temperature due to the increased surface acidity/basicity. Conversely, the Mn-substituted CeO2 NBs with the higher lattice oxygen mobility effectively accelerated the in situ decomposition of acetates/alcoholates and facilitated the re-exposure of surface active sites. This study may contribute to a further mechanistic understanding into the catalytic oxidation of esters or other oxygenated volatile organic compounds over CeO2-based catalysts.

Rationally tailored redox ability of Sn/γ-Al2O3 with Ag for enhancing the selective catalytic reduction of NO x with propene.

The development of excellent selective catalytic reduction (SCR) catalysts with hydrocarbons for lean-burn diesel engines is of great significance, and a range of novel catalysts loaded with Sn and Ag were studied in this work. It was found that the synergistic effects of Sn and Ag enabled the 1Sn5Ag/γ-Al2O3 (1 wt% Sn and 5wt% Ag) to exhibit superior C3H6-SCR performance. The de-NO x efficiency was maintained above 80% between 336 and 448 °C. The characterization results showed that the presence of AgCl crystallites in the 1Sn5Ag/γ-Al2O3 catalyst helped its redox ability maintain an appropriate level, which suppressed the over-oxidation of C3H6. Besides, the number of surface adsorbed oxygen (Oα) and hydroxyl groups (Oγ) were enriched, and their reactivity was greatly enhanced due to the coexistence of Ag and Sn. The ratio of Ag0/Ag+ was increased to 3.68 due to the electron transfer effects, much higher than that of Ag/γ-Al2O3 (2.15). Lewis acid sites dominated the C3H6-SCR reaction over the 1Sn5Ag/γ-Al2O3 catalyst. The synergistic effects of Sn and Ag facilitated the formation of intermediates such as acetates, enolic species, and nitrates, and inhibited the deep oxidation of C3H6 into CO2, and the C3H6-SCR mechanism was carefully proposed.

Lattice Compressive Strain of Co3O4 Induced by Synthetic Solvents Promotes Efficient Oxidation of Benzene at Low Temperature.

A series of Co3O4 with different surface defective structures were prepared by the solvothermal method and tested for the activity of benzene oxidation. The characterizations revealed that the synthetic solvent had a dramatic effect on the composition of Co3O4 precursors as well as the physicochemical properties of Co3O4. Although all Co3O4 exhibited a cubic spinel structure, Co3O4 prepared with triethylene glycol (Co-TEG) had the highest compressive strain due to the nature of high viscosity of triethylene glycol. These in turn affected the surface chemical structure and the low-temperature redox properties. Co-TEG exhibited the best benzene oxidation activity and showed excellent stability and good water resistance. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to study the oxidation process of benzene. It was found that Co-TEG with more defective structures had abundant surface adsorbed oxygen and active lattice oxygen, which promoted the conversion of benzene and the corresponding intermediates at low temperature.

Promotion Mechanism of CaSO4 and Au in the Plasma-Assisted Catalytic Oxidation of Diesel Particulate Matter.

Plasma-assisted catalysis has been demonstrated to be an innovative technology for eliminating diesel particulate matter (DPM) efficiently at low temperature (≤200 °C). Moreover, past studies have demonstrated that CaSO4, which exists in small concentrations (<2%) in DPM and is toxic in thermal catalytic oxidation processes, actually enhances DPM oxidation during plasma-assisted catalytic processes. However, the role CaSO4 plays in this promotion of DPM oxidation still remains unclear. The present study addresses this issue by investigating the underlying mechanisms of DPM oxidation during plasma-assisted catalytic processes using graphitic carbon as a surrogate DPM material in conjunction with CaSO4- and Au-impregnated γ-Al2O3 catalysts. The results of mass spectrometry and in situ diffuse reflectance infrared Fourier transform spectroscopy, which employs an in situ cell with a small dielectric barrier discharge space over the catalyst bed, demonstrate that CaSO4 can save and release O atoms contributing to graphite oxidation via the -S=O units of CaSO4 through a reversible surface reaction (-S=O + O → -S(-O)2). The results are employed to propose a formal mechanism of graphite oxidation catalyzed by CaSO4 and Au. These findings both improve our understanding of the plasma-assisted catalytic oxidation mechanisms of DPM and support the development of efficient plasma-assisted catalysts.

High ratio of Ce3+/(Ce3++Ce4+) enhanced the plasma catalytic degradation of n-undecane on CeO2/γ-Al2O3.

n-Undecane (C11) is the main component of volatile organic compounds (VOCs) emitted from the printing industry, and its emission to the atmosphere should be controlled. In this study, a dielectric barrier discharge reactor coupled with CeO2/γ-Al2O3 catalysts was used to degrade C11. The effect of the chemical state of CeO2 on C11 degradation was evaluated by varying the CeO2 loading on γ-Al2O3. The C11 conversion and COx selectivity were as high as 92% and 80%, respectively, under mild reaction conditions of energy density 34 J/L and 423 K to degrade 134 mg/m3 C11 in a simulated air using 10 wt%CeO2 impregnated on γ-Al2O3. After analyses using in-situ plasma diffuse reflectance Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry, it was found that most of C11 were degraded to CO2, and the main by-products on catalyst surfaces were alcohols and ketones. It was concluded from X-ray photoemission spectroscopy that the good performance of the 10 wt%CeO2/γ-Al2O3 catalyst was due to its high Ce3+/(Ce3++Ce4+) ratio as well as the oxygen vacancies. The Ce3+/(Ce3++Ce4+) ratio of CeO2 on γ-Al2O3 is crucial for the degradation of C11, providing a further roadmap for the plasma catalytic oxidation of alkanes.

Exploring the roles of oxygen species in H2 oxidation at ß-MnO2 surfaces using operando DRIFTS-MS.

Understanding of the roles of oxygen species at reducible metal oxide surfaces under real oxidation conditions is important to improve the performance of these catalysts. The present study addresses this issue by applying a combination of operando diffuse reflectance infrared Fourier transform spectroscopy with a temperature-programmed reaction cell and mass spectrometry to explore the behaviors of oxygen species during H2 oxidation in a temperature range of 25-400 °C at ß-MnO2 surfaces. It is revealed that O2 is dissociated simultaneously into terminal-type oxygen (M2+-O2-) and bridge-type oxygen (M+-O2--M+) via adsorption at the Mn cation with an oxygen vacancy. O2 adsorption is inhibited if the Mn cation is covered with terminal-adsorbed species (O, OH, or H2O). In a temperature range of 110-150 °C, OH at Mn cation becomes reactive and its reaction product (H2O) can desorb from the Mn cation, resulting in the formation of bare Mn cation for O2 adsorption and dissociation. At a temperature above 150 °C, OH is reactive enough to leave bare Mn cation for O2 adsorption and dissociation. These results suggest that bare metal cations with oxygen vacancies are important to improve the performance of reducible metal oxide catalysts.

Silencing the lncRNA NORAD inhibits EMT of head and neck squamous cell carcinoma stem cells via miR­26a­5p.

Cancer stem cells are closely associated with tumor metastasis or recurrence. According to previous literature reports, microRNA (miR)­26a has an inhibitory effect on head and neck squamous cell carcinoma (HNSCC), and the long non­coding RNA (lncRNA) non­coding RNA activated by DNA damage (NORAD) has been found to interact with miR­26a­5p. The present study aimed to investigate the regulation and mechanism of NORAD and miR­26a­5p in the epithelial­mesenchymal transition (EMT) of HNSCC stem cells. An ALDEFLUOR stem cell detection kit, a flow cytometer, a self­renewal ability test and western blotting were used to sort and identify HNSCC stem cells. The ENCORI website and a dual­luciferase assay were used to assess the relationship between genes. The mRNA and protein expression levels of NORAD, miR­26a­5p and EMT­related genes were detected via reverse transcription­quantitative PCR and western blotting. Functional experiments (MTT assay, flow cytometry, wound healing assay and Transwell assay) were conducted to analyze the effects of NORAD and miR­26a­5p on HNSCC stem cells. The successfully sorted aldehyde dehydrogenase (ALDH)+ cells had a self­renewal capacity and displayed upregulated expression levels of CD44, Oct­4 and Nanog. NORAD knockdown, achieved using small interfering (si)RNA, downregulated the expression levels of tumor markers in ALDH+ cells. siNORAD inhibited cell vitality, migration and invasion, as well as promoted apoptosis, increased the expression of epithelial cell markers and decreased the expression of interstitial cell markers in HNSCC stem cells. miR­26a­5p was a downstream gene of NORAD, and knockdown of miR­26a­5p partially offset the regulatory effect of siNORAD on HNSCC stem cells. Collectively, the present study demonstrated that NORAD knockdown attenuated the migration, invasion and EMT of HNSCC stem cells via miR­26a­5p.

Evaluation of Au/γ-Al2O3 nanocatalyst for plasma-catalytic decomposition of toluene.

The emission of toluene into the atmosphere can seriously affect the environmental quality and endanger human health. A dielectric barrier discharge reactor filled with a small amount of Au nanocatalysts was used to decompose toluene in He and O2 gases mixtures at room temperature and atmospheric pressure. Normally, the oxidation of toluene using Au nanocatalysts suffers from low reaction activity and facile catalyst deactivation. Herein, the effects of Au loading, calcination time and calcination temperature were systematically investigated. It was found that 0.1 wt%Au/γ-Al2O3 calcined at 300 °C for 5 h can keep an average size around 6 nm with good dispersion on γ-Al2O3 surface and display the best catalytic performance. Moreover, the influences of energy density, gas flow rate, toluene concentration and O2 concentration on toluene degradation using 0.1 wt%Au/γ-Al2O3 were evaluated. It showed the best catalytic performance of near 100% conversion for toluene degradation under the reaction conditions of the energy density was 20 J/L, the gas flow rate was 300 mL/min, the concentration of toluene was 376 mg/m3 and the oxygen content was 10%. Combining experimental results and theoretical calculations, the values of reaction constant k were 8.6 × 10-5, 3.53 × 10-5 and 3.09 × 10-5 m6/(mol*J), when O2 concentration, power or flow rate changed, respectively. Therefore, O2 concentration has the greatest effect on toluene decomposition compared to other factors in the presence of Au/γ-Al2O3.

Effect of supports on plasma catalytic decomposition of toluene using in situ plasma DRIFTS.

Plasma catalysis technology has been demonstrated to be effective for the decomposition of volatile organic compounds (VOCs). It is highly desired to explore the effect of supports on VOCs oxidation processes during plasma catalysis. In this work, four supports of SiO2, ZSM-5-300, ZSM-5-38 and γ-Al2O3 loading with transition metal oxides were used to decompose toluene at room temperature. It was found that toluene decomposition with 1 wt%Mn/γ-Al2O3 was highest, which was strongly proportional to the ozone decomposition ability of the catalyst. The plasma catalytic decomposition of toluene over 1 wt% MnO2 on different supports were characterized using in situ plasma diffuse reflectance infrared Fourier transform spectrometer. The results showed that 1 wt%Mn/γ-Al2O3 could further catalyze toluene to carbonate and bicarbonate via the breakage of C-C bonds from benzoic acid, while that was difficult for 1 wt% Mn/SiO2, 1 wt%Mn/ZSM-5-300 and 1 wt%Mn/ZSM-5-38. The reaction mechanism of toluene decomposition on different catalysts were proposed.

High-efficiency and low-carbon remediation of zinc contaminated sludge by magnesium oxysulfate cement.

Electroplating sludge is classified as a hazardous waste due to its extremely high leachability of potentially toxic elements. This study concerns the use of magnesium oxysulfate cement (MOSC) for the stabilisation/solidification (S/S) of Zn-rich electroplating sludge. According to X-ray diffraction and thermogravimetric analyses, Zn was mainly immobilised through both chemical interaction and physical encapsulation in the MOSC hydrates of 5Mg(OH)2·MgSO4.7H2O (5-1-7) phase. The crystal size analysis, elemental mapping, and extended X-ray absorption fine structure (EXAFS) analysis proved that the Zn2+ was also incorporated in the structure of 5-1-7 phase. Unlike Portland cement system, hydration kinetics, setting time, and compressive strength of the MOSC system were only negligibly modified by the presence of Zn, indicating its superior compatibility. Subsequent S/S experiments demonstrated that the MOSC binder exhibited an excellent performance on immobilisation efficiency of Zn (up to 99.9%), as well as satisfying the requirements of setting time and mechanical strength of sludge S/S products. Therefore, MOSC could be an effective and sustainable binder for the treatment of the Zn-rich industrial wastes.

Mechanism on the plasma-catalytic oxidation of graphitic carbon over Au/γ-Al2O3 by in situ plasma DRIFTS-mass spectrometer.

Plasma-catalytic oxidation of particulate matter (PM) has potential applications for diesel exhaust cleaning. There is a grand requirement to explore the mechanism of carbonaceous PM oxidation for the development of plasma catalysts. Herein, Au/γ-Al2O3 was used to catalyze the gasification of the graphitic carbon. A modified diffuse reflectance infrared Fourier transform spectrometer equipped with a mass spectrometer was originally utilized to in situ characterize the surface intermediates of graphite on Au/γ-Al2O3 and the gaseous products during the discharges processes in the O2-He balanced gases. It was found that O atoms and O3 play important roles in the formation of surface oxygen complexes (SOCs) and facilitate the gasification of SOCs to CO2 in the presence of Au/γ-Al2O3. The findings are helpful to understand the plasma-catalytic oxidation mechanism of PM and further develop efficient plasma catalysts.

Highly efficient decomposition of toluene using a high-temperature plasma-catalysis reactor.

Plasma-catalysis technologies (PCTs) have the potential to control the emissions of volatile organic compounds, although their low-energy efficiency is a bottleneck for their practical applications. A plasma-catalyst reactor filled with a CeO2/γ-Al2O3 catalyst was developed to decompose toluene with a high-energy efficiency enhanced by the elevating reaction temperature. When the reaction temperature was raised from 50 °C to 250 °C, toluene conversion dramatically increased from 45.3% to 95.5% and the energy efficiency increased from 53.5 g/kWh to 113.0 g/kWh. Conversely, the toluene conversion using a thermal catalysis technology (TCT) exhibited a maximum of 16.7%. The activation energy of toluene decomposition using PCTs is 14.0 kJ/mol, which is far lower than those of toluene decomposition using TCTs, which implies that toluene decomposition using PCT differs from that using TCT. The experimental results revealed that the Ce3+/Ce4+ ratio decreased and Oads/Olatt ratio increased after the 40-h evaluation experiment, suggesting that CeO2 promoted the formation of the reactive oxygen species that is beneficial for toluene decomposition.

Mechanism of CO2-formation promotion by Au in plasma-catalytic oxidation of CH4 over Au/γ-Al2O3 at room temperature.

The plasma-catalytic oxidation of methane (CH4) is a potential reaction for controlling CH4 emissions at low temperatures. However, the mechanism of the CH4 plasma-catalytic oxidation is still unknown, which inhibits the further optimization of the oxidation process. Herein, a CH4 oxidation mechanism over an Au/γ-Al2O3 catalyst was proposed based on our experimental findings. CH4 is first decomposed to CH3 and H by the discharge, and a fraction of the CH3 is adsorbed on γ-Al2O3 surface for deep oxidation. The oxygen atoms produced by the discharge react with H2O to yield surface reactive OH groups that contribute to the CH3 oxidation. Oxygen atoms also promote the release of H2O from the surfaces of the γ-Al2O3 and Au/γ-Al2O3 and especially promote CO2 desorption from the surface of the Au/γ-Al2O3. When γ-Al2O3 was used as the catalyst, the CO2 selectivity was only 15 vol.%, and the CH4 conversion decreased after 7 h of plasma-catalytic oxidation. In contrast, when Au/γ-Al2O3 was used, the CO2 selectivity was 80 vol.%, long-term CH4 conversion was obtained. Experimental results revealed that Au was beneficial for the decomposition of surface carbonate species into gaseous CO2, whereas the carbonate species accumulated on γ-Al2O3 when Au was absent.

Promotion of graphitic carbon oxidation via stimulating CO2 desorption by calcium carbonate.

Carbon oxidation has two stages, the first is the formation of surface oxides and the second is the gasification of the surface oxides to CO2. Calcium carbonate (CaCO3) was used to catalyze the gasification of the surface oxides. The catalytic effect of on graphite oxidation and its catalytic mechanism were studied by using thermogravimetric technique and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that characteristic temperature (T50) of graphite oxidation with CaCO3 was 946 K, 113 K lower than that of graphite only. DRIFTS analysis results show that surface oxides (adsorbed CO2 and carbonate CO32-) were formed on the graphite surface at a temperature above 473 K, carbonate products on graphite surface disappeared when CaCO3 was present; formation of CO32- on CaCO3 surface was confirmed, this CO32- may be more easily gasified into gaseous CO2. The kinetic analysis results showed that CaCO3 promoted graphite oxidation has an activation energy of 74.3 kJ mol-1, far lower than that of graphite (148 kJ mol-1).

Plasma-catalyst hybrid reactor with CeO2/γ-Al2O3 for benzene decomposition with synergetic effect and nano particle by-product reduction.

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO2/γ-Al2O3 catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO2/γ-Al2O3; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O3 catalyst reactor with the same CeO2/γ-Al2O3 catalyst, indicating that O3 plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O3 adsorption on CeO2/γ-Al2O3 promotes the production of adsorbed O2- and O22‒, which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO2/γ-Al2O3 catalyst. H2O inhibits benzene decomposition; however, it improves CO2 selectivity. The deactivated CeO2/γ-Al2O3 catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO2/γ-Al2O3 catalyst was proposed.

Enhanced oxidation of naphthalene using plasma activation of TiO2/diatomite catalyst.

Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO2/diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO2/diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and COx selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO2/diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO2, while the presence of ozone enhanced the activity of the TiO2/diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO2/diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.