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Methane abatement pathways in Pd/Rh three-way catalysts have been investigated in three scales ranging from a vehicle application size catalyst, a model gas reactor and the catalyst in powder form. A special test rig was designed for the investigation of vehicle size catalysts, allowing sampling along the catalyst at discrete spatial locations, which are subject to different feed compositions. Dependent on the history of chemical environment of the catalyst, significant differences in methane conversion rate at identical feed have been identified. At steady state methane conversion rate was low and the reaction pathway was identified as limited to only direct oxidation by oxygen. Following a rich-to-lean transition, the catalyst exhibited more than 8 times higher methane conversion rates compared to steady state. The high methane conversion rates have been identified and attributed to the activation of methane steam reforming (SR) related to transient reduction of ceria. Methane SR efficiency decreased with time and the conversion rate finally converged to steady state levels. The findings were validated using a model gas reactor enabling analysis under well-defined feed compositions. The deactivation of SR was further analyzed with infrared spectroscopy (DRIFTS). Evidences from DRIFTS measurements showed that the deactivation was linked to the formation of carbonaceous species on the catalyst surface, most likely carbonates. The coherent results from engine exhaust analysis, model gas reactor and DRIFTS study give important insights in the activation and deactivation of methane reaction pathways. The results of this study suggest that catalyst formulation and operation strategies of methane conversion should focus on the stimulation of SR and the maintenance of catalyst activity towards SR through targeted periodic lean/rich transitions.

The solid superacid TiO2-ZrO2-SO42−-supported 20 wt.% CeO2 catalyst (20CeO2/Ti-Zr-S) was synthesized for selective catalytic reduction of NO with NH3 (NH3-SCR). The NH3-SCR performance was significantly enhanced by the construction of strong acid sites on the surface of 20CeO2/Ti-Zr-S and over 96% NO conversion was obtained at 225–425 °C. Meanwhile, the strong interaction between solid superacid and CeO2 resulted in excellent redox property and abundant surface oxygen species. Furthermore, the NH3-SCR reaction over 20CeO2/Ti-Zr-S catalyst mainly followed the Langmuir-Hinshelwood mechanism at low-temperature (250 °C). The M-NO2 (M = Ce, Ti, Zr) nitrate compounds, monodentate and bridging nitrates were the crucial intermediates in Langmuir-Hinshelwood mechanism. In addition, amide (–NH2) species were available at 350 °C over 20CeO2/Ti-Zr-S catalyst, which facilitated the high-temperature NH3-SCR activity via Eley-Rideal pathway.

An investigation of the adsorptive property of hydrated cement particle system for sulfur dioxide (SO2) removal was conducted. In situ and ex situ experiments using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and X-ray Absorption Near Edge Spectroscopy (XANES) characterization techniques were employed to identify surface species formed during the exposure to SO2. Oxidation of SO2 to sulfate and sulfite species observed during these experiments indicated dominant reaction pathways for SO2 reaction with concrete constituents, such as calcium hydroxide, which were also moderated by adsorption on porous surfaces of crushed aggregates. The impact of variable composition of concrete on its adsorption capacity and reaction mechanisms was also proposed in this work.

In this paper, the in situ DRIFTS technology was employed to study the adsorption and reaction behavior of propylene oxide on different substances at different temperatures. And the adsorption behavior of the products at a certain temperature was also studied. The studies shows that the propylene oxide rearrangement involves thermal and catalytic transformation above 200 °C. In the first case, two main reaction pathways are involved: gradual rearrangement to the final products and pyrolysis leading to the formation of different products. In the former situation, the epoxy ring of propylene oxide first adsorbs on the basic lithium phosphate catalyst. Then it forms an intermediate with the bond between C O and C–O. The intermediate is finally converted to the final products, i.e., allyl alcohol at 300 °C. When the products (propyl aldehyde and acetone) adsorb on the catalyst, a conjugated structure consisting of basic lithium phosphate and α-H generates.

Improving catalytic efficiency is a yet still challenge in thermal catalytic oxidation. One of the key issues is to understand its catalytic oxidation mechanism. Here, a series of Co3O4 samples were prepared by solvothermal method. The characterization records showed that nanotubular Co3O4-NTs-2 for its rough surface, low temperature reducibility, abundance of Co3+ ions and surface adsorption oxygen species, thus exhibited high efficiency (T90 = 240℃, Ea = 67.42 kJ/mol) in catalytic oxidation of toluene. In-situ DRIFTS combined PTR-TOF-MS were applied to investigate the reaction process of toluene oxidation. These results revealed that the catalytic oxidation of toluene followed the listed way: toluene → benzyl alcohol → benzaldehyde → benzoate → benzene → phenol → benzoquinone → maleic anhydride and other ring opening by-products like ethanol, acetaldehyde, acetic acid, acetone etc., then ultimately mineralized to CO2 and H2O. Furthermore, the results of quasi in-situ XPS in C7H8/N2, toluene conversion in O2-free evaluation and UV–vis-DRS analysis further confirmed that surface lattice oxygen played an important role in toluene oxidation, and gas-phase oxygen facilitated the reaction. The combination of a series of instruments provided a promising means for further understanding the oxidation mechanism of toluene.

The NH3 selective catalytic reduction (SCR) performance of MnCr2O4 was shown to be greatly enhanced by doping zirconium to form Zr0.05Mn0.95Cr2O4 in our previous study. In this work, the active sites and reaction mechanisms of the catalysts were further investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations in this work. The total quantities of Lewis acid and Bronsted acid sites of Zr0.05Mn0.95Cr2O4 became 3.5 times higher than that of MnCr2O4, and various nitrate species were detected on the surface, which are beneficial for the promotion of SCR activity below 250 °C. The catalytic reactions over MnCr2O4 mainly occur between NH3 adsorbed on Cr cations and monodentate nitrates/adsorbed NO2 on Mn cations below 250 °C, and NH3 on Cr cations and gaseous NO above 250 °C, while the nitrites and N2O22− species are not reactive. The reactions between NH3 adsorbed on Mn and Zr cations and nitrates/adsorbed NO2 are the dominant pathways over Zr0.05Mn0.95Cr2O4 at all temperatures, and NH4+ species enrichment (4.3 times higher) contributed to the enhanced catalytic activity below 250 °C. DFT calculation show that when species including NH3, NH2, NO, and NO2 adsorb on Zr0.05Mn0.95Cr2O4, they yield lower adsorption energies than on MnCr2O4, and the energy barrier for NH2 and NO2 formation is also remarkably decreased. These two energy advantages facilitate conducive intermediate formation and the catalytic reactions.

Currently, selective catalytic reduction (SCR) of NOx with NH3 in the presence of alkali metal ions by using vanadium-free catalysts is still a big challenge for the removal of NOx for stationary sources. In this work, improved reduction of NOx with NH3 in the presence of alkali metal ions over novel Fe-doped manganese oxide octahedral molecular sieve (OMS-2) catalysts has been demonstrated and the promotional effects of Fe have been clarified. The Fe-doped OMS-2 (Fe-OMS-2) catalysts exhibited excellent NH3-SCR activity, improved N2 selectivity and enhanced alkali resistance. The X-ray absorption fine structure spectroscopy (XAFS) results indicated that the trapped K+ ions could make the catalyst structure more stable. In situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTs) results revealed that the Fe doping could enhance adsorption of NH3 species and adsorb various types of NOx species namely monodentate nitrate, bridged nitrate, bidentate nitrate and chelating nitrite. These formed intermediates on the Fe-OMS-2 catalysts were more reactive and thus more effectively participated in the SCR reactions. Superior alkali resistance of the Fe-OMS-2 catalysts was due to improved redox species, more acid sites and stronger adsorption of NOx species. The present investigations in this work may lead to an alternative development of high-performance non-vanadium catalysts for alkali-resistant NOx reduction.

A study of structural and mechanistic investigation of the Sb/V/Ce/Ti catalysts sulfated at different temperatures was carried out by X-ray absorption near edge spectroscopy (XANES) and diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS). The high temperature sulfated catalyst, especially Sb/V/Ce/Ti-S500 (sulfated at 500 °C temperatures), exhibited superior NO x conversion at low temperatures (150–200 °C) compared to Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300 (sulfated at 400 and 300 °C) catalysts. The Ce L 3 edge XANES spectra of Sb/V/Ce/Ti-S500 catalyst showed the formation of Ce(III) dominant sulfate species, resulting in the enhancement of Lewis and Bronsted acid strength. The formation of Ce(III) sulfate species on Sb/V/Ce/Ti-S500 catalyst was clearly indicated by Ce M 4,5 and S K edge XANES spectra peaks at 881.9 eV attributed to Ce 3+ oxidation state and 2481 eV assigned to S 6+ oxidation state of sulfate species. Furthermore, the in situ DRIFTS results revealed that the Lewis and Bronsted acid sites of Sb/V/Ce/Ti-S500 catalysts increased significantly, followed by Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S300. At 200 °C, the reaction between the pre-adsorbed NH 3 species with NO + O 2 on sulfated catalysts exhibited the formation of mono-dentate, bi-dentate, bridging nitrates and NO 2 species. Meanwhile, the subsequent formation of NO 2 via NO oxidation was promoted on Sb/V/Ce/Ti-S400 and Sb/V/Ce/Ti-S500 catalysts, followed by surface interaction with adsorbed NH 3 to produce N 2 and H 2 O at low temperatures (

We have developed the next generation of photocatalytic testing to observe the gas-phase photocatalytic reactions in situ. It is based on modified Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) unit equipped with the Smart Collector system. We have employed UV diode coupled with fiber optics to illuminate the sample while simultaneous collecting the diffuse reflectance spectra. This method was applied to study the NO2 photocatalytic conversion on nanosize gold modified TiO2 samples. We have successfully demonstrated that both gas phase and surface adsorbed species can be identified and used to compare activities of various catalysts. We have found that gold nanoparticles have significantly increased the activity of the catalysts for both gas phase and liquid phase oxidation, resulting in more than quadrupling the NO2 photocatalytic conversion in the gas phase.

Four CeO2–ZrO2 mixed oxides with different morphologies were synthesized using hydrothermal (polyhedra, rods and plates) and coprecipitation method (disordered). Detail structural/physio-chemical characterizations, catalytic activity measurements as well as in situ DRIFTS were conducted on the obtained ceria-zirconia as well as its supported Rh-only TWCs. The CeO2-ZrO2 mixed oxides present different exposed crystal planes and the catalytic performance of Rh/CeO2-ZrO2 is closely related to such different microstructures. Polyhedra shaped CeO2-ZrO2 exhibits increased lattice micro-strain originated from lattice distortion and defects, which can promote the mobility of bulk oxygen species to the surface, resulting in better three-way performance. Disordered Rh/CeO2-ZrO2 catalyst with high surface area and OSC shows wider static operation window, but the surface rhodium species tend to exist as Rh4+ with low redox ability which not favorable for the redox reactions. Besides, the lack of intermediate Rh-(NO)2 and Rh-CN species over disordered Rh/CeO2-ZrO2 based on in situ DRIFTS further reveals its unsatisfactory performance for NOx conversion.

The presence of SO3 severely affects not only the safe and economic operation of coal-fired power plants but also the atmospheric environment. The purpose of this study was to investigate the generation of SO3 over V2O5-WO3/TiO2 catalysts. The SO3 generated during the reaction was collected by the controlled condensation method. N2 adsorption, X-ray fluorescence (XRF), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), SO2 temperature-programmed desorption (SO2-TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to evaluate the catalyst properties. The experimental results show that the generation of SO3 on the catalyst is complicated and can be promoted by NO and NH3. The generation rate of SO3 increased from 0.5 vol% to 3.29 vol% with an increase in the NO concentration from 0 to 1000 ppm. When 500 ppm NH3 was added to an atmosphere containing 500 ppm NO, the generation rate of SO3 increased from 2.23 vol% to 4.23 vol%. The addition of NH3 led to a significant reduction in the specific surface area of the catalyst due to the generation of ammonium bisulfate (ABS). In addition, the results show that the proportion of lattice oxygen (Oα) and the adsorption of SO2 on the catalyst would be promoted by NO and NH3, and DRIFTS experiments further proved that NO and NH3 promoted the generation and transformation of the intermediate products VOSO4 and HSO4−.

A series of Co0.2CexMn0.8-xTi10 (x = 0, 0.05, 0.15, 0.25, 0.35 and 0.40) oxides catalysts were prepared by the sol-gel method and used for NH3-SCR. These catalysts were characterized by means of XRD, SEM-EDS, H2-TPR, NO/NH3 oxidation, NH3 (NO and SO2)-TPD, XPS and in situ DRIFTS. It was found that the Co0.2Ce0.35Mn0.45Ti10 catalyst showed excellent NH3-SCR activity and a broaden temperature window (180–390 °C), accompanied with good resistance to SO2 and H2O. It could be concluded that the redox ability of Co0.2Ce0.35Mn0.45Ti10 could be reduced by Co and Ce doping, which resulted in high NH3-SCR activity at high temperature and good resistance of SO2. The addition of Co and Ce can supply more acid sites and NOx adsorption sites over Co0.2Ce0.35Mn0.45Ti10. Thus, more surface Bronsted acid and Lewis acid sites, NOx adsorption sites and modest redox ability of Co0.2Ce0.35Mn0.45Ti10 play key roles in the special NH3-SCR activity due to the interactions among Ce, Co, Mn and Ti oxides. Furthermore, the results of in situ DRIFTS study reveal the NH3-SCR reactions over Co0.2Ce0.35Mn0.45Ti10 and Co0.2Mn0.8Ti10 catalysts are mainly controlled by E-R mechanism (>210 °C) and the L-H mechanism (

Montmorillonite based porous clay heterostructures modified with Fe (Fe-PCH) catalysts were prepared by ion exchange and impregnation methods, respectively. The PCH samples were characterized by XRD, BET, UV-vis, HRTEM, XPS, H2-TPR, Py-FTIR, etc. The catalytic activity of the catalysts was evaluated for the selective catalytic reduction of NO with C3H6 with a fixed-bed reactor and the in situ DRIFTS study was conducted to investigate the reaction mechanism. It was observed that the catalysts prepared by impregnation methods were more reactive for the SCR-C3H6, e.g., 96% of NO conversion to N2 was tested at 400 °C when 8.4 wt% iron was supported on the PCH. The results of catalyst characterization indicated that α-Fe2O3 nanorods formed in PCHs channels and (1 1 0) and (1 0 4) planes exposed. α-Fe2O3 nanorods promoted the formation of the Lewis acid sites. With the study of DRIFTS, a reaction mechanism was proposed, where the reaction intermediates were mainly inorganic nitrates, acetates, organic nitrogen compounds and isocyanate species.

MnOx was supported on peracetic acid modified coconut shell activated carbon (MnOx/AC) via facile in-situ redox reactions and used for catalytic oxidation of HCHO which is a major indoor air pollutant. The MnOx/AC catalysts were characterized by XRD, Raman, XPS, BET and in-situ DRIFTS technologies. The prepared MnOx was δ-type structure with poor crystalline. With the addition of methanol as a reducing agent during preparation, the MnOx/AC-methanol catalyst exhibited superior catalytic activity and stability toward HCHO oxidation at room temperature. The HCHO removal efficiency was kept nearly at 100% for a reaction time of 1000 min and remained highly stable even after six repetitive cycles. The rich Mn3+ and surface oxygen groups were beneficial for the catalytic activity. The in-situ DRIFTS results showed lower accumulation and faster decomposition of intermediates on the surface of the MnOx/AC-methanol catalyst, which may account for its superior catalytic efficiency and stability.

Two-dimensional (2D) materials have attracted tremendous attention as denitration catalysts for the selective catalytic reduction (SCR) reaction. Here, we prepare two-dimensional (2D) vermiculite (VMT)-supported copper–cobalt–cerium catalyst (CuCoCe/2D-VMT) by the impregnation method and employed it for the CO-SCR reaction. The NO conversion utilizing CuCoCe/2D-VMT achieves 100% at 300°C with a GHSV of 102,000 h−1in the presence of 1 vol% O2 and 5 vol% H2O. CuCoCe/2D-VMT promotes the dispersion of the active metal-site species and boosts the reduction temperature, reduces the particle size gradually. Additionally, the in situ DRIFTS spectrum reflects the existence of Cu+−CO, νas (CO32−), νs (NO3−), (NO)2, νas (–OH), νas (COO–), and δ (HCO3−) intermediates on the CuCoCe/2D-VMT surface, it supports the following mechanism study. Further, in the DFT calculation, the transition state search and potential energy analysis, CuCoCe/2D-VMT possesses lower activation energy and higher energy gain compared with CuCo/2D-VMT in each potential reaction pathway. Largely, combined with in-situ DRIFTS and the transition-state analysis, the elementary reactions of CuCoCe/2D-VMT in the SCR pathways are proposed under the following harsh conditions: CO + NO + O2 + H2O. The elementary reactions mainly includes the generation of Ov, the NO + NO process, the reaction pathways of CO reacts with *O, *OH, *H (H2O) and Ov is refilled by gaseous O2. We expect this strategy to promote the development and utilization of CO-SCR catalysts and reveal a new inexpensive and highly efficient method for practical applications.

Selective catalytic reduction (SCR) of NO with C3H6 was investigated on porous clay heterostructures modified with CuFe2O4 (CuFe-PCH). The catalysts were characterized by XRD, HRTEM, H2-TPR, XPS, Py-FTIR and in situ DRIFTS technologies. CuFe-PCH showed high SCR activity at low temperature. Among all the catalysts in this study, Cu1Fe-PCH with the molar ratio of Cu:Fe = 1:1 exhibited the best catalytic performance, which reached 58.5% NO removal at 300 °C (0.1%C3H6) and 100% NO removal at 350 °C (0.3%C3H6) respectively. The active components on CuFe-PCH catalyst were mainly CuFe2O4 nanocrystal, exposing (2 2 0) and (3 1 1) planes. The CuFe2O4 species on Cu1Fe-PCH had high crystallinity, good redox ability, large proportion of lattice oxygen, high density of acid sites and strong Bronsted acidity, which were all responsible for the highest C3H6-SCR activity. By in situ DRIFTS, more isocyanates, including Cu-NCO and Fe-NCO, were found on Cu1Fe-PCH, which were beneficial to enhance C3H6-SCR activity. Finally, a possible reaction path was proposed.

A mechanistic-based kinetic model is developed for selective catalytic reduction of NO with C 3 H 6 on Cu chabazite (Cu-SSZ13) monolithic catalyst based on bench scale flow reactor studies and in-situ DRIFTS measurements. The SCR mechanism involves reaction between oxygenates (partially oxidized hydrocarbon species) and NO to form isocyanates species ( NCO), detected by DRIFTS, which are further reduced to N 2 . We have shown in an earlier study that reaction intermediates, most likely surface isocyanates, poison the active sites on the catalytic surface resulting in the inhibition of other reactions (Raj et al., 2013 [7]). The kinetic model was developed in steps, starting with steady-state CO oxidation, followed by C 3 H 6 oxidation, and then the C 3 H 6 + NO + O 2 reaction system. This approach ensured consistency in the parameter estimation and resulted in a more robust model. The models for CO + O 2 , C 3 H 6 + O 2 and C 3 H 6 + NO + O 2 were also validated using a new set of steady state experiments. The monolith model predicts the observed negative order with respect to C 3 H 6 and positive order with respect to O 2 for the C 3 H 6 oxidation reaction. For the C 3 H 6 + NO + O 2 reaction system, the predicted NO and C 3 H 6 conversions agree well with both steady state and transient experimental data. The model captures the significant shift of C 3 H 6 light-off to higher temperature in the presence of NO due to formation of the inhibiting NCO surface species as well as slow transients associated with surface intermediates and their effect on the extent of reactions.

A series of ternary composite oxide catalysts CuO/CO3O4-CeO2 with variable Ce/(Co + Ce) atomic ratios were prepared and employed for the preferential oxidation of CO (CO PROX). Many techniques such as N-2-sorption, XRD, H-2-TPR, O-2-TPO, CO-TPD, O-2-TPD, Cu K-edge XAFS (including EXAFS and XANES) and in situ DRIFTS were used for catalyst characterization. The catalyst CuO/CO3O4-CeO2 with Ce/(Ce + Co) ratio of 0.1 exhibits the best performance, showing not only the lowest temperature for the complete oxidation of CO (98 degrees C), but also the broadest operating temperature window for full CO conversion (98-173 degrees C). The results of N-2-sorption and temperature-programmed characterizations including H2-TPR, O-2-TPO, CO-TPD and O-2-TPD show that the CuCoCe10 catalyst possesses the highest BET surface area, the best reducibility/oxidizability and the best performance for CO and O-2 adsorption. Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cu species including Cu-0, Cu+ and Cu2+ species co-exist in the spent catalyst CuCoCe10. Stable Cu+ carbonyl species are identified as the main active reaction intermediates as revealed by in situ DRIFTS. High temperature (>120 C) can lead to the reduction of Cu+ to Cu-0, enhancing H-2 oxidation; as a result, the selectivity of O-2 towards CO2 is decreased. Based upon in situ DRIFTS results, a potential CO PROX mechanism over CuO/CO3O4-CeO2 catalysts is proposed. (C) 2013 Elsevier B.V. All rights reserved.

A series of hydrotalcite-derived K/MnMgAlO catalysts were synthesized by co-precipitation and impregnation methods. Their catalytic performances for soot combustion, NOx storage and simultaneous soot-NOx removal were evaluated, respectively. Techniques of TG/DTA, BET, XRD, EXAFS, and in situ DRIFTS were employed for catalyst characterization. The catalyst K/Mn1.5Mg1.5AlO containing 7.5 wt% K shows not only the highest soot oxidation rate of 58.0 mu gs(-1) per gram catalyst, but also the maximal NOx reduction percentage of 26.9%. Over the catalysts containing K less than 10 wt%, the soot combustion follows oxygen spillover mechanism, while over those containing more than 10 wt% K it follows a different mechanism involving the participation of potassium nitrate species. In situ DRIFTS results indicate that introduction of proper amount of K can facilitate the formation of monodentate nitrate, which shows higher reactivity with soot than nitrite, chelating bidentate nitrate and ionic nitrate species. In the catalysts promoted by K, a new phase namely K2Mn4O8 was identified, which is highly active for soot combustion and NOx reduction by soot. (C) 2012 Elsevier B.V. All rights reserved.

Publisher Copyright: © 2022 The Author(s) Pd/SSZ-13 catalysts were investigated for the simultaneous storage of NO and C3H6 at 100 °C. The effects of the state of Pd species on co-adsorption and release were studied under simulated exhaust conditions. The catalysts were characterized by NH3-TPD, XRD, and TEM for Pd2+ and PdO species. NO adsorption/release behavior is impacted by the nature of reactants and the NO storage capacity at 100 °C was enhanced by simultaneous NO + C3H6 adsorption. DRIFTs results showed that Pd2+ provides the adsorption sites for NO + C3H6 to form Pd2+(NO)(C3H6), which alleviates the inhibition effect of H2O on NO adsorption on Pd ions. Different release behaviors, which are discussed in light of the chemistry of NO and C3H6 adsorption and effect of intermediate CO, depend on whether NO was adsorbed alone or together with C3H6. The mechanistic pathways during different stages of NO + C3H6 co-adoption and release are proposed.

The design of advanced catalysts for CO2 methanation remains as a research challenge. Besides, the effects of feed composition on the activity and stability of existed catalysts are not well addressed yet. In this work, novel A2BO4-type catalysts derived from La2−xCexNiO4 perovskites are reported for CO2 methanation. The reduced La0.5Ce1.5NiO4 (r-La0.5Ce1.5NiO4) sample with tailored oxygen vacancies, higher reducibility, better Ni dispersion, and exposed Ni(111) crystal plane exhibited the highest CO2 conversion of 78.9% and 99.3% CH4 selectivity at 350 °C, which can also endure different H2/CO2 ratios and even up to 50 %v/v steam. Interestingly, the activity and structure of spent r-La0.5Ce1.5NiO4 can be fully recovered after 100 h TOS under 10 %v/v steam. In-situ DRIFTS experiments confirmed CO2 methanation over the r-La0.5Ce1.5NiO4 to proceed via CO route. The present work suggests that both basicity and the presence of oxygen vacancy facilitate superior catalytic activity and stability during CO2 methanation.

The selective oxidation of H2S, which can eliminate H2S and recover sulfur as a useful resource, is a promising strategy because of its low capital cost and thermodynamically unlimited nature. However, there are obstacles in the development of stable and efficient catalysts to meet the needs of practical cases. Herein, we disclose the use of porous MIL-100(Fe) with coordinatively unsaturated (CUS) Fe2+/Fe3+ sites (denoted as CUS-MIL-100(Fe)) as efficient and stable catalyst for H2S removal. The catalyst is prepared via a simple hydrothermal process using iron powder and 1,3,5-benzenetricarboxylates (H3BTC) as raw materials, and its physicochemical properties have been studied by XPS, BET, ICP-OES, EPR, XRD, and in-situ DRIFTS techniques. The results reveal that the desulfurization performance of the CUS-MIL-100(Fe) catalyst is higher than that of commercial Fe2O3, achieving near 100% H2S conversion and 100% S selectivity at 100–190 °C. Importantly, the H2S conversion and S selectivity over CUS-MIL-100(Fe) are 100% and 95.1% in a continuous run of over 100 h, while those of Fe2O3 are only 42.6% and 19.4% after 13 h. This can be ascribed to the unique characteristics of CUS-MIL-100(Fe), such as the presence of Fe2+/Fe3+ CUSs, large specific surface area, and regular pore structure.

Diesel engine exhaust has been identified to be highly carcinogenic. In order to improve the control of diesel engine exhaust emissions, the diesel engine oxidation catalyst (DOC) + catalytic diesel particulate filter (CDPF) + selective catalytic reduction catalyst (SCR) + NH3 oxidation catalyst (ASC) united technology has become the mainstream technology for catalytic aftertreatment. Perovskite oxides have emerged as a promising catalyst for NO oxidation and can be used as the DOC. Undoped La2MMnO6 (M = Co, Fe, Ni, Cu) double perovskites, A-site Ba-doping (La2-xBax)CoMnO6 (%Ba = 0, 25%, 50%, 75%, 100%) perovskites and B-site Cu-doping La2Co1-yCuyMnO6 (y = 0, 0.25, 0.50, 0.75, 1) double perovskites were prepared by a facile molten-salt synthesis method and examined by XRD, SEM, BET, in situ DRIFTS, and XPS. In addition, we calculated the B-site ionic magnetic moments of the double perovskites μ which were contributed by the effective Bohr magneton number n p of the B-site 3d transition metal ions, such as Mn3+, Mn4+, Co3+, Fe3+, Ni2+, and Cu2+. The correlations between the B-site ionic magnetic moments and the maximum NO conversion over all those double perovskites were also calculated. The B-site ionic magnetic moments has a strong positive correlation with the highest conversion rate of NO catalytic oxidation over all those double perovskites. That is, the higher the B-site ionic magnetic moments, the better the catalytic oxidation performance of NO over the double perovskites. So enhancing the B-site ionic magnetic moments by A-site doping is a method to improve the catalytic activity of NO oxidation over the perovskites. Increasing the B-site ionic magnetic moments is the key index to improve the catalytic activity of NO oxidation of the double perovskites by B-site doping.

Magnesium oxide (MgO) with different morphologies was prepared by oxalic acid sol-gel method and the MgO were used to prepare three different kinds of adsorbents for simultaneous SO2 and NOx removal from coal-fired flue gas. It was found that the core-shell coated adsorption material MgO@CeO2-MnOx prepared from MgO formed by calcination of magnesium oxalate at 650 ℃ had the best performance. The MgO@CeO2-MnOx exhibited an adsorption breakthrough time up to 50 min and dynamic adsorption capacity of 0.3507 mmol/g and 0.1407 mmol/g for SO2 and NOx respectively. This is better than any other composite material. The N2 adsorption-desorption isotherms result showed that core-shell structure material possessed the largest specific surface area, which could be its basic advantage for efficient adsorption. According to different operating conditions tests, it was found that the adsorption of SO2 and NOx by the adsorbent was dominated by chemisorption. Therefore, the surface metal material (MnOx, CeO2) played an important role in the adsorption process. According to FTIR and DRIFTS analysis, it was observed that the SO2 and NO were oxidized by hydroxyl groups on the absorbent surface and the oxidation was further aggravated by the presence of Mn4+, Mn3+, Ce3+and Ce4+. Core-shell materials successfully prepared can reduce or weaken the adsorption competition between SO2 and NOx in three aspects: 1. The surface oxidation ability is strengthened and it is easy to adsorb the two substances, which makes the metal oxides on the shell surface interact fully with the adsorbents; 2. More and more effective adsorption sites are provided; 3. The adsorbent provides greater specific surface area and appropriate pore size.

Catalytic removal of NO by CO has been studied over a series of LaNi0.5M0.5O3 (M = Co, Mn, Cu) perovskite oxide catalysts were synthetized via an improved sol–gel method. The effects of M-doped on physicochemical properties of LaNiO3 were systemic characterized by XRD, BET, SEM, ICP-AES, XPS, H2-TPR and O2-TPD techniques. The possible catalytic mechanism for NO + CO model reaction was also tentatively proposed with the help of the in situ DRIFTS technique. The M-doped samples remained pure perovskite structure and exhibited modified activity, among which the LaNi0.5Cu0.5O3 possessed optimized catalytic performance, especially superior N2 selectivity. It is confirmed that the amorphous CuO highly dispersed on Cu-doped defective perovskite oxide, the reduction of Cu2+ to Cu+ is vital for the chemisorption of CO, a large amount of oxygen vacancies accelerated the dissociation of NO and N2O. Hence, adsorbed CO can fast react with N and O at lower temperature, afterwards N2O was converted to N2 fleetly, leading the improvement of activity/selectivity toward NO + CO reaction.

In the present work, we chose MnOx/CeO2-ZrO2 nanorod (i.e., Mn/CZ-NR) as a benchmark catalyst, and used TiO2 as a modifier with the purpose of inhibiting the formation of N2O (by-product) as well as further enhancing the catalytic activity and H2O + SO2 tolerance of Mn/CZ-NR catalyst. These samples were characterized by TEM, HRTEM, XRD, Raman, H2-TPR, XPS, NH3-TPD, and in situ DRIFTS. DeNOx performance and H2O + SO2 tolerance of these samples were evaluated by low-temperature NH3-SCR reaction. The obtained results show that the TiO2 modified catalyst (i.e., Mn-Ti/CZ-NR) exhibits higher catalytic activity than Mn/CZ-NR catalyst due to larger amount of oxygen vacancy accompanied with more Ce3+, higher ratios of Mn4+ and surface adsorbed oxygen species, as well as the improvement of surface acidity. Furthermore, TiO2 modification effectively inhibits the non-selective oxidation of NH3 to N2O through appropriately weakening the redox property of Mn/CZ-NR catalyst, which is beneficial to the enhancement of N2 selectivity. Finally, Mn-Ti/CZ-NR catalyst exhibits excellent H2O + SO2 tolerance, which indicates that it has the potential to be used for practical low-temperature deNOx application.

The effect of Ce or La on the hydrothermal stability of Cu-SAPO-34 catalyst was evaluated by the selective catalytic reduction of NOx by ammonia (NH3-SCR) reaction after hydrothermal aging at 700 °C in 10 vol% H2O/air for 10 h. The hydrothermal stability of Cu-SAPO-34 was dramatically enhanced by introducing small amount Ce or La into Cu-SAPO-34. More than 93% NOx conversion was maintained over the aged Ce or La modified Cu-SAPO-34 at 175–350 °C, while extremely poor NH3-SCR activity was obtained over the aged Cu-SAPO-34. In situ diffuse reflection infrared Fourier transform spectrum (DRIFTS) results illustrated that the hydrothermal treatment cut off the intrinsic “E-R” reaction route over the Cu-SAPO-34 and opened the new reaction pathway (“L-H” mechanism) over the La modified Cu-SAPO-34 catalyst. Additionally, the introduction of Ce or La effectively mitigated the dealumination progress and restrained the aggregation of copper species over Cu-SAPO-34 during the hydrothermal aging, further maintaining the relatively large specific surface area and uniform pore size distribution. Meanwhile, the incorporation of Ce or La enhanced the redox property and stabilized the surface acid sites of Cu-SAPO-34, further facilitating the adsorption and activation of reactants.

Manganese oxides with different valences (MnO2, Mn2O3 and Mn3O4) synthesized by a hydrothermal synthesis method were investigated to evaluate their catalytic performances for NO oxidation. MnO2 with the Mn4+ ion exhibited the best catalytic activity with a maximum NO conversion of 91.4% at 250 °C under the GHSV of 48 000 mL g−1 h−1, and the low-temperature catalytic activity for NO oxidation decreased in the order of MnO2 > Mn2O3 > Mn3O4. Compared with Mn2O3 and Mn3O4, the catalytic performance of MnO2 was less affected by NO concentrations, O2 contents, GHSV, H2O and SO2, though all the three catalysts show stable catalytic properties. To investigate the factors influencing the catalytic activity, their properties were characterized by XRD, SEM, N2 adsorption, H2-TPR, O2-TPD and XPS, and these results indicated that the redox property and active oxygen species of MnO2 were proposed to be the main factors that contributed to the excellent performance in NO oxidation. For the three catalysts, in-situ DRIFTS studies further indicated that both the lattice oxygen and the chemically adsorbed oxygen participated in the NO oxidation process, but the adsorbed species were more easily desorbed from MnO2, probably benefiting for the catalytic performance of MnO2.

SO2 and CO2 emitted from using of fossil fuels are causing serious environmental issues. Herein we put forward a promising strategy to realize CO2 reduction and SO2 removal simultaneously through a photoelectrochemical (PEC) process based on nanoelectrodes. In the present work, SO2 was oxidized to SO42− on BiVO4 photoanode after being absorbed by NaHCO3 solutions. At the same time, CO2 reduction occurred on nanoflower-like copper-indium alloy cathode. The absorption efficiency of SO2 was greater than 95%, and SO32− was oxidized to SO42− with oxidation efficiency about 50% in 3 h. Moreover, the energy of SO2 was recycled to assist the CO2 reduction on the cathode, consequently, the photocurrent densities were increased at least 3 times after introducing SO2. CO2 reduction with CO and HCOOH as main products was improved significantly when SO2 removal was conducted simultaneously. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were also performed to study the adsorption and conversion of SO2 on BiVO4 nanoparticles. The proposed approach could efficiently remove SO2 and recycle the energy of it to reduce CO2 into useful chemicals. This work provides a sustainable strategy for dealing with CO2 and SO2 in the flue gas by combining desulfurization and CO2 reduction in one PEC cell using nanoelectrodes.

The precise regulation of the nano-catalyst structure is a big challenge that limits the application of photocatalytic technology in CO2 reduction. Herein, to improve the utilization of sunlight, the separation and transfer efficiency of photogenerated electron-hole pairs, and the surface catalytic reaction process, CuInS2/C/TiO2 (CIS/C/T) hierarchical tandem heterostructure have been rationally designed. Multiple in-situ characterizations and DFT simulations show that CQDs not only act as a co-catalyst, but also act as a bridge between TiO2 (T) and CuInS2 (CIS), which further attribute to the efficient separation and enrichment of photogenerated electron-hole pairs while effectively avoiding the recombination. In consideration of the excellent broad-spectrum absorption, the CO2-to-CO photoreduction performance of the optimal CIS/C/T reaches up to 7.73 μmol g-1 h-1, about 3.16 times enhancement of C/T. Combined with in-situ DRIFTs, the intrinsic structure-activity relationship is pointed out, and extended to other similar TiO2-based catalytic systems (In2S3/C/TiO2). This work will provide a new universal strategy for the design and synthesis of high-performance nano-photocatalysts.

Synthesis of methyl methacrylate (MMA) via direct oxidative esterification from methacrolein (MAL) and methanol (MeOH) is of great significance in chemical industry. Supported gold catalysts are considered as one of the most potential candidates for this reaction but suffer from low activity and deactivation issue. Herein, by modulating the phase structure of hydroxyapatite (HAP) with different cations and anions, a synergic effect between gold and vanadate substituted hydroxyapatite (HVP) support for the synthesis of MMA was discovered. In direct oxidative esterification, among the evaluated catalyst/support systems, Au/HVP catalyst displays the best performance and unprecedented stability, which acts as one of the best-performing gold catalysts for oxidative esterification. Various characterizations such as X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), transmission electron microscope (TEM) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO were conducted to disclose the structural and electronic property of the catalysts. Through in-situ FT-IR spectra of MAL and MeOH, the substrate was proved to be easily transformed on Au/HVP catalyst to ester. Besides, the presence of O2 was found to facilitate the adsorption of MAL. The results of temperature programmed desorption (TPD) of O2 implied that gold particles together with HVP support is promotional for activation and dissociation of oxygen, leading to good activity and high selectivity.

Introduction of surface oxygen vacancy (Vo) has been proved to be a powerful method to promote the performance of H2S selective oxidation by improving H2S adsorption and O2 activation. Nevertheless, maximizing the oxygen vacancy concentration remains a challenge due to limited exposed surface. Herein, we report a Fe-doped TiO2−x ultrathin nanosheet with abundant oxygen vacancies for H2S selective oxidation via a facile citric acid assisted hydrothermal process. One of the cheapest and most abundant metals, iron, is a desirable dopant for further promoting the H2S oxidation activity of TiO2. As a result, the Fe-doped TiO2−x nanosheets endowed with abundant oxygen vacancies exhibited nearly 100% H2S conversion and sulfur selectivity at 210 °C and is superior to those of most reported Ti-based materials. Furthermore, through in situ DRIFTS, in situ Raman and EPR spectra of H2S oxidation, the reaction pathway for selective oxidation of H2S over Fe-doped TiO2−x with abundant oxygen vacancies was revealed. The density functional theory (DFT) calculations were conducted to get a deeper insight into the effect of Fe-doping on the electronic structure and oxygen vacancy of defected TiO2.

A multiheterojunction structured photocatalyst FeN-CDs/TiO2@CN was prepared by a facile low temperature anneal method, which exhibits excellent photocatalytic nitrogen fixation activity. The CDs with abundant electrons and functional groups transferred electrons to active centers more effectively, and the tightly heterogeneous interface between the carbon dots/TiO2 and graphic carbon nitride improves the separation of electro-holes. In addition the coexistence of two types of TiO2 (anatase and rutile) is more advantageous for NRR compared with pure rutile or anatase TiO2. It was confirmed that FeN-CDs is the active site for nitrogen fixation reaction. The photocatalytic nitrogen fixation performance of FeN-CDs/TiO2@CN reached 9.365 mg h−1 gcat-1. Temperature-programmed desorption (N2-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed to prove the efficient adsorption and protonation of N2 over FeN-CDs. A feasible mechanism was proposed for photo-induced charge separation and nitrogen photofixation on FeN-CDs/TiO2@CN.

To identify the distinctive role of reactive oxygen species (ROS) and trace the intermediates not only help to decompose the pollutants in high efficiency but also for avoiding more harmful intermediates formed. Here, we developed a new method to generate different ROSs by controlling the atmosphere to distinguish their role in the degradation of flowing gas-phase VOCs, including o-xylene, styrene, and acetaldehyde. This method is in good agreement with the traditional sacrificial agent capture experiment. The results show that •OH radicals play a dominant role in the degradation of o-xylene and styrene, while •O2− radicals primarily take part in the acetaldehyde degradation. Additionally, we distinguish the role of holes, •OH and •O2− played during the VOCs photo-oxidation through the radical trapping, in situ DRIFTS, and GC-MS analysis. Under the attack of •O2− radicals, aromatic VOCs were photo-oxidized to intermediates containing benzene rings and ketones (i.e., toluene and butanone), while carbon chain compounds (i.e., 3-methylfuran and ethanol) tend to form under the action of •OH and holes. This can be associated with the different reaction paths initiated by ROS. For acetaldehyde removal, •O2− species facilitate the formation of acids (i.e., acetic acid) while the •OH species and holes lead to the production of ketones (i.e., acetone). This work provides deep understanding on the role of various ROS in the photocatalytic oxidation of VOCs, which can guide the design of efficient photocatalysts, selective formation of intermediates to be easily decomposed or as raw materials for further application.

Kinetic aspects of the operating parameters for the catalytic conversion of H2/CO2 to methanol over two novel catalysts were evaluated to understand the effect of the polymorphic ZrO2 phase composed of Cu0/+-ZnO sites at the atomic level and its impact on the reaction mechanism. The catalysts were characterized by in situ and ex-situ XRD, N2 adsorption/desorption isotherms, FRX, TPR, TPD-N2O, in situ XANES, TPD-CO2, and in situ DRIFTS techniques. The influence of different reaction variables such as the GHSV, temperature, pressure, and H2/CO2 ratio were studied using a fixed bed continuous plug flow reactor. The Cu-ZnO catalyst supported on the tetragonal zirconia polymorph exhibited the highest methanol yield due to the lower activation energy when compared to the catalyst with a greater amount of the monoclinic phase. In addition, the catalysts were reused for 8 cycles of 6 h to evaluate their stability, which can translate into lower costs for large-scale methanol production. The estimation of the kinetic parameters for the Cu-Zn oxide catalysts supported on ZrO2 polymorphs was important to understand the reaction mechanism, as well as to provide useful information for scaling up the process.

Highly active platinum (Pt)-based nanostructured materials are expected as catalysts to effectively mineralize recalcitrant aromatic volatile organic compounds (e.g., benzene) even at low temperature conditions. In this regard, the utility of a titanium dioxide (TiO2) supported Pt (1 wt%) catalyst was explored for the thermocatalytic oxidation of benzene in the air. The superior performance of Pt/TiO2-R (‘R’ denotes the high-temperature hydrogen-based reduction pre-treatment of the catalyst) over its non-reduced counterpart was attributed to the increase in metallic Pt (Pt0) nanoparticles present on the TiO2 surface alongside strong metal-support interactions (SMSIs). The SMSIs at the Pt-TiO2 interface partially reduced the metal oxide structure to generate Ti3+ centers, giving rise to oxygen vacancies. The analysis of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the benzene molecules are oxidized into carbon dioxide via phenolate, benzoquinone, carboxylate, and carbon monoxide intermediates. The present study offers new insights into the application of Pt-based high-performance catalysts for achieving complete removal of benzene at low temperatures.

Plasma catalysis technology has shown a great prospect in the oxidation of volatile organic compounds with a low concentration. However, low energy efficiency and large numbers of nanoparticle by-products are still the bottleneck for its practical application. Herein, a dielectric barrier discharge (DBD) reactor coupled with nano-sized Au (0.1 wt%) supported on γ-Al2O3 (denoted as Au/γ-Al2O3) was used for plasma catalytic oxidation of toluene. It was found that the energy efficiency was 89.5 g*kWh−1 at 25 °C, and improved to 125.0 g*kWh−1 at 250 °C. If a catalyst was not used in the DBD reactor, the by-products including benzaldehyde, phenol and benzoic acid were formed during the toluene oxidation. Those by-products can form nanoparticles which cause another risk to the atmosphere and human beings. With the use of Au/γ-Al2O3 nanocatalyst, the emission of nanoparticle by-products was reduced by 99.99%. Meanwhile, in-situ plasma DRIFTS analysis showed that Au-based catalysts can promote the oxidation of by-products and the gasification of carbonates to CO2.

By varying divalent-metal cations (M = Mg2+, Ni2+, Cu2+, Zn2+) with different d-bands classification, MAl-LDHs were prepared and inspected for solar-driven CO2 conversion. The CO and CH4 yields over these LDHs followed an order of: NiAl-LDHs > CuAl-LDHs > ZnAl-LDHs > MgAl-LDHs. Coupled with multiple characterizations, the activity distinction was revealed from three crucial perspectives: (i) light harvesting, (ii) charge separation and transfer, (iii) surface reactions. The results affirmed that when d orbital was partially occupied with active electrons, both activation of CO2 and excitation of electrons were much easier to achieve. In-situ DRIFTS manifested that NiAl-LDHs and CuAl-LDHs exhibited more active reaction with CO2, which may be related to the upward shifts of the d-band center determined by Valence-band XPS. Particularly, these LDHs exhibited various catalytic stabilities, which was explained by Pearson׳s hard and soft acid–base (HSAB) principle for the first time in this field.

Uniform mesoporous iron titanium (CT-FeTi) catalysts were synthesized by a CTAB-assisted process and exhibited good catalytic activity and H2O resistance when tested in the selective catalytic reduction (SCR) of NO with NH3 at low temperature. BET, TPD, TPSR and in situ DRIFTS were carried out to reveal the inhibition mechanism of H2O on SCR reaction and determine the role of CTAB in the improved H2O resistance during low-temperature SCR processes. Results showed that H2O inhibited the adsorption of NO on the surface of CT-FeTi catalysts, as well as the formation of the intermediate species (–NH2), which was produced by the reaction Fe 3+ + NH 3 → Fe 2+ - NH 2 + H + . CTAB acted as a “structural” and “chemical” promoter, not only optimizing the pore size to avoid being excessively enlarged in the presence of H2O, but also enhancing the adsorption of bridging nitrate and NH3 species on Lewis acid sites, thus improving the catalytic activity and H2O resistance.

A series of Sm- and/or Zr-doped MnOx-TiO2 catalysts were prepared, and the catalysts exhibited better N2 selectivity and SO2 resistance than the undoped MnOx-TiO2 catalyst for the selective catalytic reduction of NO by NH3 (NH3-SCR). The reasons for the good N2 selectivity and SO2 resistance of the catalysts were proposed. X-ray photoelectron spectroscopy (XPS) combined with density functional theory (DFT) calculations suggested that electron transfer between the manganese and samarium species by Mn4+ + Sm2+ ↔ Mn3+ + Sm3+ redox cycles occurred in the Sm-containing catalysts. Furthermore, electron transfer from Sm2+ to Mn4+ suppressed electron transfer from NH3 to Mn4+, inhibiting the formation of NH2 or NH. Thus, the pathway for NH generation was removed, and the reaction of 2NH + 4NO → 3N2O + H2O was prevented. Consequently, the N2 selectivity of the NH3-SCR reaction was enhanced. In situ diffused reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) combined with thermogravimetry, differential scanning calorimetry and mass spectrometry (TG-DSC-MS) results revealed that the deposition rate of sulfate species decreases after Sm doping, which was also attributed to the suppressed electron transfer from SO2 to Mn4+, i.e., the oxidation of SO2 to SO3. Thus, the catalysts exhibited better SO2 resistance.

Fiber-based palladium catalysts were synthesized via an ultrasonic-assisted impregnation method on ceramic and glass fiber supports pretreated by leaching with water, sulfuric acid and nitric acid, respectively. The as-prepared catalysts were next tested for the catalytic combustion of benzene. The Pd-Ceramic fiber exhibited better activity than Pd-glass fiber in terms of benzene conversion and carbon dioxide yield, and 0.8 wt% Pd loading was the optimum loading amount. The prepared catalysts were characterized by FE-SEM, BET, XRD, XPS, TEM, in situ DRIFTS and TPD. The results indicated that a relatively large surface area, strong support acidity, well-dispersed Pd particles, and suitable redox and desorption properties all contributed to the good performance of ceramic-fiber-based catalysts. Our findings demonstrate that the Pd-Ceramic fiber catalyst is an effective candidate for application in elimination of volatile organic compounds.

Mesoporous CeO2 catalysts (CeO2-MOF) were synthesized by pyrolysis of Ce-MOF precursor (Ce-(1,3,5-benzenetricarboxylic acid) (H2O)6). Physicochemical properties of the samples were investigated by means of various techniques including XRD, SEM, TEM, BET, Raman, XPS, H2-TPR, O2-TPD and NH3-TPD, and their catalytic performance were evaluated by toluene combustion compared with commercial CeO2 (CeO2-C) and CeO2 prepared by precipitation method (CeO2-P). The results show that CeO2-MOF/350 catalyst (pyrolyzed at 350 °C) presents enhanced catalytic activity for toluene oxidation with the conversion of T10%, T50% and T90% at 180, 211, and 223 °C, respectively (SV = 20,000 mL/(g h), toluene concentration = 1000 ppm). Especially for high-temperature region, CeO2-MOF/350 catalyst displays much superior ability to rapidly reach to 100% conversion compared to CeO2-C and CeO2-P catalysts which usually result in a much broader temperature region to achieve complete conversion of toluene. The high catalytic performance of CeO2-MOF/350 can be reasonably ascribed to a series of better properties, such as three-dimensional penetrating mesoporous channels, larger specific surface area, smaller average grain size, higher relative percentages of Ce3+/Ce4+ and OSur/OLatt, higher oxygen storage capacity, higher oxygen vacancy concentration, better low temperature reducibility, more active oxygen species and more acid sites. Furthermore, CeO2-MOF/350 catalyst presented excellent resistance to H2O deactivation and temperature change, and in situ DRIFTs study on CeO2-MOF/350 catalyst suggests that toluene degradation is proceeded in consecutive steps via rapid transformation to aldehydic and benzoate species to finally form CO2 and H2O.

Mesoporous MgO adsorbents with diverse basic sites were prepared via a urea hydrolysis synthesis method for CO2 capture. With elevated hydrolysis temperatures, the phase transition process made great contributions to the morphological changes of the precursor architectures. In situ DRIFTS analysis demonstrated that various carbonate surface species including bicarbonate, bidentate, and unidentate carbonates were formed on the obtained MgO during interaction with CO2. Furthermore, the main component of adsorbed CO2 surface species swings from bicarbonate to bidentate and unidentate carbonates with increase of adsorption temperature. The highest CO2 uptake of 1.22–1.99 mmol g−1 was attained for MgO sample at the lowest calcination temperature in a wide temperature range of 60–300 °C. High specific surface area (372.0 m2 g−1), large pore volume (0.38 cm3 g−1) as well as diverse basic sites of the synthesized MgO make it an eligible candidate for CO2 capture, with a nearly 20-fold enhancement of the commercialized light MgO. Additionally, the results of CO2 uptake studied under diluted and wet (H2O containing) CO2 conditions for the as-prepared MgO adsorbent also suggested good prospect in practical applications.

Three-dimensional penetrating Pt-loaded mesoporous Cr2O3 catalysts (Pt@M-Cr2O3) were synthesized by pyrolysis of MIL-101-Cr containing pre-impregnated Pt NPs. Physicochemical properties of the samples were characterized by means of various techniques including XRD, Raman, BET, SEM, TEM, XPS and H2-TPR, and their catalytic activities were evaluated by toluene combustion compared with commercial Cr2O3 (C-Cr2O3). It is found that mesoporous Cr2O3 (M-Cr2O3) support with a high surface area of 77.40 m2/g is composed of vast Cr2O3 nanocrystallites. With pre-impregnated Pt loading in MIL-101-Cr, it partly restrains the aggregation of Pt NPs during the pyrolysis of MOFs to M-Cr2O3 and strengthens the interaction between Pt NPs and Cr2O3 nanocrystallites. The obtained 0.82Pt@M-Cr2O3 exhibits the best catalytic performance of toluene combustion, giving 120, 140 and 144 °C of T10%, T50% and T90% under 1000 ppm of toluene at space velocity of 20,000 mL/(g h), respectively. The investigation of the different space velocity, the catalytic stability and the effect of water vapor on catalytic activity over 0.82Pt@M-Cr2O3 have confirmed the good catalytic performance. Furthermore, the studies of in situ DRIFTS indicate toluene degradation over 0.82Pt@M-Cr2O3 is via benzoate species by rapidly transforming of benzylic and aldehydic species, and then oxidized to maleic anhydride in an aromatic-ring opening reaction, finally is decayed to CO2 and H2O.

Mesoporous coralloid NaInO2 was prepared through a facile secondary calcination reaction based on mesoporous In2O3. As a binary sodium transition metal oxide containing a layered structure, the application of prepared mesoporous NaInO2 for HCHO oxidation at room temperature was investigated in this study. After 1.0 wt% Pt supported, the sample possessed a high initial removal efficiencies of HCHO up to 91.4% in 15 min, as well as low final residues of less than 5.5 ppm in 60 min. The characterizations indicate that prepared mesoporous NaInO2 has abundant interface structural defects (XRD peak shifting) and substantial BET surface area of 51.9 m2/g, which may generate surface oxygen vacancies manifesting as large amounts of chemisorbed oxygen (OC/Ototal as 36.09%). According to the research results, surface oxygen vacancies might help greatly to capture gaseous HCHO molecules, where chemisorbed oxygen being a cofactor for HCHO oxidation, and then the catalyst transformed HCHO into formate, carbonate and finally CO2 indicated by in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) analysis. Overall, this study provided a promising way for designing Pt-supported catalysts for ambient air purification by introducing surface defects (oxygen vacancies) and chemisorbed oxygens.

The Mn-based catalyst with hollow spherical structure was prepared by hydrothermal method and used for selective catalytic reduction (SCR) of NO with NH3. Mn-based catalysts exhibit excellent de-NOx performance at low-temperature, but narrow operating temperature window and poor water resistance restrict its application. Effectively expanding the operating temperature window and improving the H2O resistance of the Mn-based catalyst are the keys to industrial application. In this article, the H-MnO2 catalyst was prepared by hydrothermal method and modified by kinetic adsorption and vapor deposition methods. The TiO2 layer can effectively limit the excessive redox performance and improve the acidity of the catalyst surface, the NO conversion above 90% at 140–380 °C of H-MnO2@TiO2 catalyst. The phenyltrimethoxysilane was deposited on the surface of the H-MnO2@TiO2 catalyst by vapor deposition method. The NO conversion rate of the H-MnO2@TiO2@HL catalyst exceeds 80% in the temperature range of 180–380 °C. When the H2O was introduced, the NO conversion rate increases from 70% to 85% at 180 °C. The in situ DRIFTs results showed NH3 and NO could be adsorbed and activated on the catalyst surface, and the catalytic reaction follows Langmuir-Hinshelwood (L-H) mechanism. Under the presence of H2O, the NH4+ bonding to Bronsted acid sites were inhibited but the NH3 bonding to Lewis acid site was almost unaffected. In summary, through two-step modification, the operating temperature window and water resistance of Mn-based catalysts are effectively improved. It can be seen that a reasonable structure design can effectively improve the comprehensive performance of the catalyst.

Formaldehyde (CH2O) and toluene (C7H8) are typical indoor air pollutants that have high harm to people’s health. Photocatalytic oxidation is a feasible approach, but still remains the problem of incomplete degradation to form refractory intermediates and uncertainty of interaction between multivariant components. This paper used natural proteins from waste shell as the carbon source and template to synthesize the ternary TiO2/C/MnO2 photocatalysts. It exhibited high adsorption selectivity and excellent photocatalytic performance for CH2O and C7H8 mixture mineralization under visible light irradiation. The optimal candidate achieved near completely mineralization within 60 min in the simulated indoor environment and exhibited remarkable stability after 5 cycles. Large amounts of oxygen vacancies, lattice distortions of TiO2, and tailored bandgap structure contributed to these excellent behaviors. Besides, carbon existence as an electron transfer channel dropped the interfacial charge-transfer resistance, thus prolonging the lifetime of charge carriers and making them rapidly go through the surface photo-oxidation reactions. In-situ DRIFTs results indicated that CH2O and C7H8 mixtures possessed the same reaction pathway and rate-determining step with single component. Above all, this paper offered a facile, sustainable, and green approach to synthesize efficient photocatalysts for treating indoor CH2O/C7H8 pollution with visible light irradiation.

This paper conducted catalytic ozonation and oxidation of chlorobenzene (CB) and dichloroethane (DCE) over three synthesized MnO2 catalysts with different properties. Catalytic ozonation exhibited high efficiency with less catalyst dosage at low temperature, ca. 30 ~ 120 °C, excellent stability, and less byproducts formation for both CB and DCE conversion. MnO2–I exhibited the best performance for all experiments, attributing to its abundant oxygen vacancies, more acid sites, and excellent CO2 desorption properties. Catalytic ozonation exhibited excellent stability with much fewer organic byproducts in effluent gas at 120 °C·H2O had no effect on catalytic ozonation but recovered catalytic oxidation performance. Besides, O3 existence attained high activity over deactivated catalyst by Cl poisoning. In–situ DRIFTs measurements validated facilitated transformation of intermediates during catalytic ozonation. These findings comprehensively verify the superiority of catalytic ozonation to attain highly stable and complete degradation of chlorinated volitile organic compounds (Cl–VOCs) at mild conditions.