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Precious metal catalysts with superior low-temperature activity and excellent thermal stability are highly needed in environmental catalysis field. In this work, a novel two-step incipient wetness impregnation (T-IWI) method was developed for the fabrication of a unique and highly stable CeO2/Al2O3 support (CA-T). Pd anchored on CA-T exhibited a much higher low-temperature catalytic activity and superior thermal stability in carbon monoxide (CO) and hydrocarbon (HC) oxidations, compared to Pd anchored on conventional CeO2/Al2O3 (CA), which was prepared by a one-step IWI method. After aging treatment at 800 °C, the CO oxidation rate on Pd/CA-T (1.69 mmol/(gPd s)) at 120 °C was 4.1 and 84.5 times of those on Pd/CA (0.41 mmol/(gPd s)) and Pd/Al2O3 (0.02 mmol/(gPd s)), respectively. It was revealed that the CA-T support with well-controlled small CeO2 particles (ca. 12 nm) possessed abundant defects for Pd anchoring, which created rich Pd-CeO2 interfaces with strengthened interaction between Pd and CeO2 where oxygen could be efficiently activated. This resulted in the significantly improved oxidation activity and thermal stability of Pd/CA-T catalysts. The T-IWI method developed herein can be applied as a universal approach to prepare highly stable metal oxide-alumina-based supports, which have broad application in environmental catalyst design, especially for automobile exhaust aftertreatment.

A series of BUC-21/N-K2Ti4O9 composites (B1NX) were facilely fabricated from BUC-21 and N-K2Ti4O9 via ball-milling, and they were fully characterized using various techniques. The photocatalytic reduction of Cr(VI) over the B1NX composites was investigated systematically under various conditions, including different light sources, pH values, hole scavengers, and inorganic ions, in both real lake water and tap water. The BUC-21/N-K2Ti4O9 composites demonstrated remarkable photocatalytic Cr(VI) reduction performance, good reusability, and stability under both UV and white light irradiation. The introduction of N-K2Ti4O9 into BUC-21 not only broadened its light absorption region to white light, but also strongly inhibited the recombination of the photo-generated electrons and holes. Mechanisms of photocatalytic Cr(VI) reduction under both UV light and white light were proposed and verified by electrochemical measurements, active species capture experiments, and ESR measurements.

The continuous emissions of volatile organic compounds (VOCs) from the industrial process cause serious environmental problems and pose a threat to human health. Photodegradation technology and bio...

The controlled oxidation of alcohols to the corresponding ketones or aldehydes via selective cleavage of the β-C-H bond of alcohols under mild conditions still remains a significant challenge. Although the metal/oxide interface is highly active and selective, the interfacial sites fall far behind the demand, due to the large and thick support. Herein, we successfully develop a unique Au-CuO Janus structure (average particle size=3.8 nm) with an ultrathin CuO layer (0.5 nm thickness) via a bimetal in situ activation and separation strategy. The resulting Au-CuO interfacial sites prominently enhance isopropanol adsorption and decrease the energy barrier of β-C-H bond scission from 1.44 to 0.01 eV due to the strong affinity between the O atom of CuO and the H atom of isopropanol, compared with Au sites alone, thereby achieving ultrahigh acetone selectivity (99.3 %) over 1.1 wt % AuCu

Co3O4 is an important catalyst widely used for CO oxidation or electrochemical water oxidation near room temperature and was also recently used as support for single-atom catalysts (SACs). Co3O4 with a spinel structure hosts dual oxidation states of Co2+ and Co3+ in the lattice, leading to the complexity of its surface structure as the exposure of Co2+ and Co3+ has a significant impact on the performance of the catalysts. Although it is acknowledged that different facets exhibit varied catalytic activities and different abilities in hosting single atoms to provide active centers in SACs, the Co3O4 surface structure remains under-investigated. In this study, major facets of {111}, {110}, and {100} were studied down to subangstrom scale using advanced electron microscopy. We noticed that each facet has its own most stable surface configuration. The distribution of Co2+ and Co3+ on each facet was quantified, revealing a facet-dependent distribution of Co2+ and Co3+. Co3+ was found to be preferentially exposed on {100} and {110} as well as surface steps. Surface reconstruction was revealed, where a subangstrom scale shift of Co2+ was confirmed on facets of {111} and {100} due to polarity compensation and oxygen deficiency on the surface. This work not only improves our fundamental understanding of the Co3O4 surface structure but also may promote the design of Co3O4-based catalysts with tunable activity and stability.

MnO nanoparticles supported on coal-based activated carbon (AC) were facilely fabricated via incipient wetness impregnation method by calcination of manganese acetate in nitrogen. The as-prepared catalysts were characterized by N2 adsorption-desorption, XRD, TEM, and XPS. It is demonstrated that calcination under inert atmosphere can facilely obtain well dispersed MnO nanoparticles on AC, and the particle size, as well as the surface oxygen species of the catalysts strongly depended on the calcination temperature. The AC supported MnO nanoparticles all exhibited high catalytic activity toward ozone decomposition at room temperature, and an optimal one was displayed as the calcination temperature of 700 °C. The smallest particle size of MnO nanoparticles and the most amount of surface oxygen vacancies, were mainly responsible for the highest activity of MnO/AC-700. Moreover, lower loading of Mn was found to be more favorable for stable catalytic performance. This work reported a series of MnO based catalysts for efficient removal of ozone at room temperature for the first time, and may shed new lights on the design of manganese oxides with lower oxidation state for efficient ozone decomposition.

Volatile organic compounds (VOCs), methane, carbon monoxide, soot, automotive exhaust, and nitrogen oxides are harmful to the atmosphere and human health. It is urgent to strictly control their emissions. Heterogeneous catalysis is an effective pathway for the removal of these pollutants, and the critical issue is the development of novel and high-performance catalysts. In this review, we briefly summarize the preparation methods, physicochemical properties, catalytic activities, and related reaction mechanisms for the above pollutants removal of the rare earth oxides, mixed rare earth oxide, rare earth oxide-supported noble metal, and mixed rare earth oxide-supported noble metal catalysts that have been investigated by our group and other researchers. It was found that catalytic performance was associated with the factors, such as specific surface area, pore structure, particle size and dispersion, adsorbed oxygen species concentration, reducibility, reactant activation ability or interaction between metal nanoparticles and support. Furthermore, we also envision the development trend of such a topic in future work.

Volatile organic compounds (VOCs) and methane are pollutants that are harmful to the atmosphere and human health. It is highly required to control emissions of VOCs. Catalytic oxidation is one of the most effective pathways for the elimination of VOCs, in which the key issue is the development of novel and high-performance catalysts. In this review article, we briefly summarize the preparation strategies, physicochemical properties, catalytic activities, and stability for the oxidative removal of VOCs of the supported bimetallic catalysts that have been investigated by our group and other researchers. The supported bimetallic catalysts include the supported noble bimetal, supported noble metal-transition metal, and supported non-precious bimetal catalysts. It was found that catalytic performance was related to one or several factors, such as specific surface area, pore structure, particle size and dispersion, adsorbed oxygen species concentration, reducibility, lattice oxygen mobility, acidity, reactant activation ability, and/or interaction between bimetals or between metal and support. The stability and ability of anti-poisoning to water, carbon dioxide or chlorine were related to the nature of the bimetal and support in the catalysts. In addition, we also envision the development trend of such a topic in the future work.

Supported noble metal catalysts are highly effective for eliminating volatile organic compounds (VOCs). A catalyst with less noble metal loading is always desirable. Using a mixture of NaNO3 and NaF as molten salt, Fe(NO3)3 and Pt(NH3)4(NO3)2 as metal precursors, xPt/Fe2O3 catalysts (x = 0–0.3 wt%) were fabricated after calcination at 350 °C for 3 h. At space velocity of 40,000 mL/(g h), 0.22 wt% Pt/Fe2O3 showed the best catalytic activity, and o-xylene could be completely oxidized into CO2 and H2O at 225 °C. Furthermore, 0.22 wt% Pt/Fe2O3 exhibited good stability, and high resistance to water vapor, CO2, and SO2. We deduce that the excellent catalytic performance of 0.22 wt% Pt/Fe2O3 was associated with the high dispersion of the Pt species and good low-temperature reducibility. The possible reaction mechanism of o-xylene oxidation over 0.22 wt% Pt/Fe2O3 involved the adsorption of o-xylene molecules, partial decomposition into small organic intermediates (e.g. maleic anhydride and aliphatic carboxylate species), and total oxidation into CO2 and H2O. Due to the high efficiency, good stability, low cost, and convenient preparation, the present catalysts are promising for the practical removal of VOCs.

The strong interaction between Au nanoparticles and support (Au-metal oxide interface) usually governs the performance of a supported Au catalyst in heterogeneous catalysis. In this study, a series of Au/reduced graphene oxide (rGO)/three-dimensionally ordered macroporous (3DOM) Co

We successfully prepared 1.98 wt% PtRu nanoparticles (NPs) partially embedded in the skeleton of three-dimensionally ordered macroporous Ce0.7Zr0.3O2 (denoted as 1.98PtRu@3DOM CZO) using the polymethyl methacrylate-templating and ethylene glycol reduction methods. For comparison purposes, we also synthesized a 3DOM CZO-supported 2.03 wt% PtRu catalyst (denoted as 2.03PtRu/3DOM CZO) via a colloidal adsorption route. The 1.98PtRu@3DOM CZO sample exhibited better performance than the Pt or Ru NPs partially embedded in the skeleton of 3DOM CZO. Ru played an important role in promoting the low-temperature reducibility and oxygen adsorption ability of the sample. The catalytic activity of 2.03PtRu/3DOM CZO was better than that of 1.98PtRu@3DOM CZO (ΔT90% = 23 °C) for toluene combustion, and the former showed lower apparent activation energy (45 kJ/mol). However, 1.98PtRu@3DOM CZO possessed excellent thermal stability, over which the activity did not change obviously, while that over 2.03PtRu/3DOM CZO decreased greatly; furthermore, the catalytic activity of the former was superior to that of the latter after calcination at 800 °C for 5 h. After high-temperature treatment, the average particle size of PtRu NPs in 1.98PtRu@3DOM CZO increased slightly from 4.2 to 6.7 nm, whereas that of PtRu NPs in 2.03PtRu/3DOM CZO increased significantly from 5.1 to 17.3 nm. It is concluded that the good performance of 1.98PtRu@3DOM CZO is associated with its highly dispersed partially embedded PtRu NPs and good toluene and oxygen adsorption ability, since the embedded structure facilitated formation of a larger amount of Pt O Ce-like bonds that possessed strong interaction between PtRu NPs and 3DOM CZO and hence contributed to its better thermal stability.

Mesoporous Co3O4 (meso-Co3O4)-supported Pt (0.53 wt.% Pt/meso-Co3O4) was synthesized via the KIT-6-templating and polyvinyl alcohol (PVA)-assisted reduction routes. Mesoporous CoO (meso-CoO) was fabricated through in situ reduction of meso-Co3O4 with glycerol, and the 0.18–0.69 wt.% Pt/meso-CoO samples were generated by the PVA-assisted reduction method. Meso-Co3O4 and meso-CoO were of cubic crystal structure and the Pt nanoparticles (NPs) with a uniform size of ca. 2 nm were well distributed on the meso-Co3O4 or meso-CoO surface. The 0.56 wt% Pt/meso-CoO (0.56Pt/meso-CoO) sample performed the best in benzene combustion (T50% = 156 °C and T90% = 186 °C at a space velocity of 80,000 mL/(g h)). Introducing water vapor or CO2 with a certain concentration led to partial deactivation of 0.56 Pt/meso-CoO and such a deactivation was reversible. We think that the superior catalytic activity of 0.56 Pt/meso-CoO was intimately related to its good oxygen activation and benzene adsorption ability.

The mesoporous M–Al (M = Ce, La, Co, Ce–La, and Ce–Co) catalysts were synthesized by adopting a modified “one-pot” evaporation-induced self-assembly (EISA) strategy with ultrasound or microwave irr...

Ruthenium-based materials are promising catalysts for the removal of chlorine-containing volatile organic compounds (CVOCs) due to their good ability in cleaving the C–Cl bonds and decreasing the Cl deposition. However, the roles of noble bimetals alloyed with Ru have not been clarified clearly. In this work, the bimetallic RuyM (M = Au, Pd or Pt) alloys supported on three-dimensionally ordered macroporous (3DOM) CeO2 (xRuyM/3DOM CeO2; RuyM loading (x) = 0.90–0.93 wt%, and Ru/M molar ratio (y) = 2.77–2.87) were fabricated by the polymer microbead-templating and polyvinyl alcohol-protected reduction methods, and their physicochemical properties were well measured using a number of techniques. Oxidation of trichloroethylene (TCE) was used to evaluate catalytic performance of the as-obtained samples with a good-quality 3DOM structure and a surface area of 39–44 m2 g−1. The Ru, Pd, and RuyM nanoparticles (NPs) with an average size of 2.9–3.5 nm were uniformly dispersed on the skeleton surface of 3DOM CeO2. The 0.93Ru2.87Pd/3DOM CeO2 sample showed the highest catalytic activity and the lowest apparent activation energy (34 kJ mol−1), with the temperatures (T50% and T90%) at TCE conversions of 50 and 90% being 237 and 298 °C at a space velocity of 20 000 mL g−1 h−1, respectively. Simultaneously, 0.93Ru2.87Pd/3DOM CeO2 exhibited the highest TCE oxidation rate (30.3 μmol gNoblemetal−1 s−1) and the highest TOFNoblemetal (3.1 × 10−3 s−1) at 250 °C. The 0.93Ru2.87Pd/3DOM CeO2 sample also possessed a better hydrothermal stability than the 0.85Ru/3DOM CeO2 sample after hydrothermal ageing treatment at 750 °C. Effects of H2O, CO2, and HCl on catalytic activity of 0.93Ru2.87Pd/3DOM CeO2 were also examined. The presence of Ru in the samples was favorable for generation of HCl and Cl2 and reduction of the by-products in TCE oxidation, and tetrachloroethylene was the main by-product. The possible catalytic mechanism over 0.93Ru2.87Pd/3DOM CeO2 was also proposed. The outstanding catalytic efficiency of 0.93Ru2.87Pd/3DOM CeO2 could be assigned to the high adsorbed oxygen species, good low-temperature reducibility, strong TCE adsorption and activation ability, and formation of the intimate nanointerface between RuPd NPs and 3DOM CeO2. This work provides a practical guideline for rationally designing the efficient bimetallic catalysts for CVOCs removal under the industrial conditions.

Improving the low-temperature water-resistance of methane combustion catalysts is of importance for industrial applications and it is challenging. A stepwise strategy is presented for the preparation of atomically dispersed tungsten species at the catalytically active site (Pd nanoparticles). After an activation process, a Pd-O-W

The purification efficiency of auto-exhaust carbon particles in the catalytic aftertreatment system of vehicle exhaust is strongly dependent on the interface nanostructure between the noble metal component and oxide supports. Herein, we have elaborately synthesized the catalysts (Pt/Fe

A novel La-Co-O-C (LC-C) composites were prepared via a facile co-hydrothermal route with oxides and glycerol and further optimized for methane catalytic activity and thermal stability via component regulation. It was demonstrated that Co

Ru-based catalysts for catalytic combustion of high-toxicity Cl-containing volatile organic compounds are inclined to produce Cl

Self-prepared beaded activated carbons (SBAC) were derived from carbonized phenolic formaldehyde (PF) resins through an optimal activation procedure (900 o C for 4 h) using CO 2 . A commercial BAC (termed KBAC) was adopted to compare with SBAC over physicochemical properties, adsorption performance against methyl ethyl ketone (MEK) and toluene (TOL), and the regenerability using microwave irradiation. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models showed good fitting results to explain the adsorption equilibrium. The isosteric heat of adsorption was calculated using the Clausius-Clapeyron equation; the parameters obtained from the D-R isotherm indicate that the interactions between adsorbate and adsorbent were mainly due to physisorption. Microwave heating was applied to the regeneration of saturated adsorbents to examine the effect of irradiation power and heating time on the desorption behavior of adsorbate. Within 12 min of microwave irradiation, excellent desorption efficiencies based on gravimetric method were shown, reaching 110.7 ± 14.4, 104.4 ± 2.6, 90.2 ± 2.3, and 85.5 ± 5.7% for MEK-SBAC, MEK-KBAC, TOL-SBAC, and TOL-KBAC, respectively. After an 8-cycle of adsorption/regeneration, the adsorption capacity for SBAC was significantly decreased when loaded with TOL, whereas it was more significant than the virgin sample as loaded with MEK. In contrast, KBAC was able to sustain the adsorption capacity after an 8-cycle of regeneration, proving its stability throughout the microwave heating. Kinetic models were further employed to illustrate the desorption of the adsorbates from BAC samples, showing that intraparticle diffusion in SBAC and KBAC was the rate-limiting step during microwave heating. The core kinetic parameters obtained could provide insights for lab-scale adsorbent beds or practical engineering scale design. In conclusion, this study demonstrates the excellent adsorption performance of SBAC and the feasibility of microwave regeneration of BACs.

Manganese oxide supported Pt single atoms (Pt1/MnOx) are prepared by the molten salt method. Catalytic oxidation of toluene and iso-hexane, typical emissions from furniture paints industry, is tested. Pt1/MnOx shows poor and high catalytic stability for toluene and iso-hexane oxidation, respectively. Enhancement in the catalytic stability for toluene oxidation is observed after the hydrogen reduction treatment of Pt1/MnOx at 200 °C. The hydrogen treated catalyst possesses the weaker Mn–O bonds and lower coordination number of Pt O, with superior mobility of lattice oxygen and appropriate toluene adsorption. Balancing lattice oxygen mobility and volatile organic compounds adsorption is important for the catalytic stability of Pt1/MnOx. For the oxidation of toluene and iso-hexane mixture, owing to the competitive adsorption, iso-hexane oxidation is greatly inhibited, while toluene oxidation is not influenced. The present Pt1/MnOx catalyst holds promising prospect in furniture paints industry applications because of high catalytic stability and water resistance ability.

The KIT-6-templating and polyvinyl alcohol-protected NaBH4 reduction methods were adopted to prepare the mesoporous manganese oxide (meso-MnOy) and its supported Co, Pt, and PtxCo catalysts, respectively. Numerous techniques were used to characterize the physicochemical properties of the materials. Catalytic performance of the samples was evaluated for methanol combustion. All of the samples possessed a three-dimensionally ordered mesoporous structure and a surface area of 94–110 m2/g. The Co, Pt, and PtxCo nanoparticles (NPs) with an average size of 2.2–3.0 nm were uniformly dispersed on the surface of meso-MnOy. The 0.70 wt% Pt2.42Co/meso-MnOy sample performed the best: the T50% and T90% (temperatures required for achieving methanol conversions of 50 and 90%, respectively) were 50 and 86 °C at a space velocity of 80,000 mL/(g h). The partial deactivation of the 0.70Pt2.42Co/meso-MnOy sample due to water vapor or carbon dioxide introduction was reversible. It is concluded that the excellent catalytic activity of 0.70 wt% Pt2.42Co/meso-MnOy was associated with its highly dispersed Pt2.42Co alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pt2.42Co alloy NPs and meso-MnOy.

Mesoporous 55 wt.% Ni/MgO and group VIB metal (Cr, Mo or W)-doped catalysts were prepared using the facile "one-pot" evaporation-induced self-assembly in ethanol and wetness impregnation methods, respectively. Physicochemical properties of the as-prepared catalysts were characterized by means of the BET, XRD, SEM, TEM, HAADF, XPS, H2-TPR, TPO, and Raman techniques. The doping of Cr to 55 wt% Ni/MgO improved catalytic activity and stability for the decomposition of methane under harsh reaction conditions. The maximal initial methane conversions of 80, 87, and 75% were achieved over the 55 wt.% Ni−xCr/MgO (denoted as 55Ni−xCr/MgO; x = 5, 10, and 15 wt.%) at 675 oC and GHSV = 48,000 mL/(g h), respectively. It is concluded that the high catalytic efficiency of the Cr-doped sample in methane decomposition was associated with its high surface area, high oxygen adspecies concentration, and good low-temperature reducibility. In addition, multi-walled carbon filaments with metal-encapsulated carbon particles were deposited on the Cr-doped catalysts, and the ordered carbon filaments with different diameters and good crystallinity were produced on the surface of the 55Ni−10Cr/MgO catalyst.

The concurrent production of COx-free hydrogen and multi-walled carbon filaments by thermocatalytic decomposition of methane is advantageous in the environmental and energy catalysis. In the present work, a facile “one-pot” evaporation-induced self-assembly strategy was effectively adopted to fabricate the nickel catalysts supported on mesoporous Al2O3, SiO2, TiO2, and MgO, and their catalytic activities for methane decomposition were evaluated for the first time. The structural, textural, and redox properties of the as-obtained materials were characterized using a number of analytical techniques. The nitrogen sorption analysis indicated the presence of a mesoporous structure due to homogeneous aggregation of the catalyst particles with a high specific surface area of 32–236 m2/g. Among all of the catalysts, Ni/MgO exhibited the best catalytic activity for methane decomposition (65% methane conversion at 600 °C and GHSV of 48,000 mL/(g h)). The activity increased when Ni loading increased from 25 to 55 wt%. The investigation on the correlation between catalytic performance and promoter doping effect suggests that incorporating copper into the MgO support considerably enhanced the catalytic activity and stability at high temperatures. The XPS results reveal that doping of Cu to Ni/MgO enhanced the adsorption and activation of oxygen molecules. In addition, the disordered crystalline carbon filaments with different diameters and good crystallinity were generated on the surface of the Cu-doped Ni/MgO catalysts.

Volatile organic compounds (VOCs) cause damage to atmospheric environment and human health. Supported noble metal catalysts are widely used to control VOCs emissions. The high cost, and low H2O-, CO2-, and SO2-resistance of such catalysts are worthy to be improved. Herein we fabricated Ce-, V-, or W-doped TiO2 supported ultralow loading Pt catalysts via the in-situ molten salt method, and evaluated their catalytic performance for acetone (major pollutants in pharmaceutical industry) removal. Under the present reaction conditions, all the catalysts exhibited high catalytic activity and stability for acetone oxidation, with the temperature required 90% acetone conversion being of 245 °C over 0.57 wt% CeO2-0.05 wt% Pt/TiO2. The doping of Ce, V, or W enhanced the H2O-, CO2-, and SO2-tolerance ability of 0.05 wt% Pt/TiO2. More than 85 %85%, 70%, or 60% of acetone could be removed even in the presence of 20 vol% water vapor, 10 vol% CO2, or 100 ppm SO2, respectively. The improvement in SO2-tolerance ability was due to the inhibition of SO2 adsorption and oxidation activity as well as Ti(SO4)2 or TiOSO4 formation. Acetone complete oxidation over 0.57 wt% CeO2-0.05 wt% Pt/TiO2 would follow the pathway: adsorbed acetone molecules → acetic acid and formic acid → carbonate species → CO2 and H2O. The present supported Pt catalysts might be suitable for oxygenated VOCs removal.

Single-atom catalysts are a kind of promising catalytic materials that can use the precious metal more efficiently. The KIT-6-templaing method was adopted to obtain three-dimensionally ordered mesoporous iron oxide (meso-Fe2O3). The meso-Fe2O3-supported single-atom Pt with a loading of x wt% (xPt1/meso-Fe2O3, x = 0.08, 0.15, and 0.25) catalysts were synthesized via a polyvinyl alcohol-protected reduction route. The 0.25 Pt1/meso-Fe2O3 sample showed much better catalytic activity than the meso-Fe2O3-supported Pt nanoparticle (0.25 PtNP/meso-Fe2O3) sample for benzene combustion, with the temperatures T10%, T50%, and T90% (corresponding to benzene conversions of 10, 50, and 90%) were 164, 186, and 198 °C at a space velocity of 20,000 mL/(g h), respectively. The TOFPt (2.69 s−1) obtained over 0.25 Pt1/meso-Fe2O3 at 160 °C was much higher than that (1.16 s−1) obtained over the 0.25 PtNP/meso-Fe2O3 sample at 160 °C. Furthermore, the 0.25 Pt1/meso-Fe2O3 and 0.15Pt1/meso-Fe2O3 samples exhibited better water-resistant ability than the 0.25 PtNP/meso-Fe2O3 sample, which was possibly due to formation of the active radicals and decomposition of carbonates in the presence of moisture. In situ DRIFTS results demonstrate that the phenolate and benzoquinone as well as cyclohexanone and maleate were the main intermediates in the oxidation of benzene. The good stability of the 0.15Pt1/meso-Fe2O3 and 0.25 Pt1/meso-Fe2O3 samples was associated with the strong interaction between Pt and meso-Fe2O3.

The xCo3O4–MnO2 (x = 2.6, 8.8, and 13.3 wt%) catalysts were prepared using the polymethyl methacrylate microspheres-templating, incipient wetness impregnation, and acid treatment methods. Physicochemical properties of the samples were characterized by means of various techniques. Catalytic performance of the xCo3O4–MnO2 samples was evaluated for the combustion of o-xylene. It is shown that the as-prepared samples possessed a cubic crystal structure and a surface area of 51.9–63.9 m2/g. The 8.8Co3O4–MnO2 sample possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility, and hence performing the best: the T10%, T50%, and T90% (temperatures required for achieving o-xylene conversion of 10, 50, and 90%, respectively) were 231, 251, and 273 °C at a space velocity of 100,000 mL/(g h). The apparent activation energies obtained over the xCo3O4–MnO2 catalysts for o-xylene combustion were 72–82 kJ/mol. The effects of space velocity, water vapor, and carbon dioxide on the catalytic activity of the 8.8Co3O4–MnO2 sample were also examined, and the partial deactivation due to water vapor and carbon dioxide introduction was reversible. It is concluded that the good catalytic performance of 8.8Co3O4–MnO2 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Co3O4 and MnO2.

Since the conventional Pd-based catalysts often suffer severe deactivation by water, development of a catalyst with good activity and moisture-resistance ability is of importance in effectively con...

An effective praseodymium oxysulfate/Ba0.5Sr0.5Co0.8Fe0.2O3-δ composite cathode with high stability in 10% CO2/air was investigated. The addition of 50 vol.% of the praseodymium oxysulfate shows much better tolerance to CO2, and reduced the polarization resistance of the cathode to 1/3 comparing with that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). The CO2–temperature programmed desorption (TPD) and the electrochemical impedance spectroscopy (EIS) proved the effectiveness of the praseodymium oxysulfate phase to reduce the electrode resistance and to improve the CO2 resistance. The coefficient thermal expansion (CTE) rate along with the different volume percentage of praseodymium oxysulfate was also measured and it was found that the praseodymium oxysulfate helps to regulate the total CTE of the composite to match with doped-ceria electrolyte. It is proposed the higher acidity of Pr3+/4+ cations inhibited the reaction of alkaline earth metal oxide to form carbonates on the surface of the BSCF particles. The above results proved praseodymium oxysulfate/Ba0.5Sr0.5Co0.8Fe0.2O3-δ to be a highly active and stable cathode for solid oxide fuel cells.

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Metal-organic framework MIL-100(Fe) and g-C3N4 heterojunctions (MG-x, x = 5%, 10%, 20%, and 30%, x is the mass fraction of MIL-100(Fe) in the hybrids) were facilely fabricated through ball-milling and annealing, and characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, UV-visible diffuse-reflectance spectrometry, and photoluminescence emission spectrometry. The photocatalytic activities of the series of MG-x heterojunctions toward Cr(VI) reduction and diclofenac sodium degradation were tested upon irradiation with simulated sunlight. The influence of different organic compounds (ethanol, citric acid, oxalic acid, and diclofenac sodium) as hole scavengers and the pH values (2, 3, 4, 6, and 8) on the photocatalytic activities of the series of MG-x heterojunctions was investigated. MG-20% showed superior photocatalytic Cr(VI) reduction and diclofenac sodium degradation performance than did the individual MIL-100(Fe) and g-C3N4 because of the improved separation of photoinduced electron-hole charges, which was clarified via photoluminescence emission and electrochemical data. Moreover, the MG-x exhibited good reusability and stability after several runs.

The removal of toxic hexavalent chromium (Cr(VI)) ions from surface and ground water is highly demanded. While photocatalytic reduction of Cr(VI) to Cr(III) by traditional powder photocatalysts is a promising method, the difficult in the separation of the photocatalysts from the water hinders their wide practical applications. Herein we present the use of metal-organic framework (MOF) UiO-66-NH2(Zr/Hf) membrane as photocatalysts to reduce Cr(VI) ions with high efficiency and easy separation from the treated waste water. The UiO-66-NH2(Zr/Hf) MOF membrane photocatalysts were fabricated via a reactive seeding method on a α-Al2O3 substrate. It was found that the UiO-66-NH2(Zr/Hf) membranes exhibited excellent photocatalytic Cr(VI) reduction performance under both simulated and real sunlight irradiation. The UiO-66-NH2(Zr) membrane can maintain more than 94% Cr(VI) reduction efficiency after 20 cycles because of its exceptional chemical and water stability. The influences of foreign ions on Cr(VI) reduction were investigated to mimic real lake water, which revealed that no obvious adverse effects can be found with the presence of common foreign ions in surface water. The MOF membrane photocatalysts provide a new approach to carry out efficiently photocatalytic removal of pollutants in wastewater.

The chemical state of Pd plays an important role in the catalytic combustion of volatile organic compounds (VOCs). In this work, we adopted a novel one-step modified KIT-6-templating strategy with nitrates of cobalt and palladium as the metal source to successfully synthesize the three-dimensionally ordered mesoporous Co3O4-supported Pd nanoparticles (0.85 wt% Pd/meso-Co3O4, denoted as 0.85Pd/meso-Co3O4). The 0.93 wt% Pd/meso-CoO (denoted as 0.93Pd/meso-CoO) and 1.08 wt% Pd/meso-Co–CoO (denoted as 1.08Pd/meso-Co–CoO) samples were prepared via in situ reduction of 0.85Pd/meso-Co3O4 in a H2 flow at 200 and 350 °C, respectively. Among these samples, 0.93Pd/meso-CoO exhibited the highest catalytic activity for benzene combustion (T50% = 167 °C and T90% = 189 °C at a space velocity of 40 000 mL (g h)−1). The chemical state of Pd on the 0.93Pd/meso-CoO surface was metallic Pd0, which favored oxygen activation to active adsorbed oxygen (Oads) species, hence rendering this sample to possess the largest desorption of Oads species below 400 °C. The intermediates of formate, acetate, maleate, and phenolate were generated via the interaction of benzene and Oads species. We conclude that the excellent catalytic performance of 0.93Pd/meso-CoO was related to the mainly formed Pd0 species, good oxygen activation ability, and high surface area.

Mn-based catalysts are expected to be applied for removing NO

Odor emissions from intensive livestock farms have attracted increased attention due to their adverse impacts on the environment and human health. Nevertheless, a systematic summary regarding the characteristics, sampling detection, and control technology for odor emissions from livestock farms is currently lacking. This paper compares the development of odor standards in different countries and summarizes the odor emission characteristics of livestock farms. Ammonia, the most common odor substance, can reach as high as 4100 ppm in the compost area. Sampling methods for point and area source odor emissions are introduced in this paper, and odor analysis methods are compared. Olfactometers, odorometers, and the triangle odor bag method are usually used to measure odor concentration. Odor control technologies are divided into three categories: physical (activated carbon adsorption, masking, and dilution diffusion), chemical (plant extract spraying, wet scrubbing, combustion, non-thermal plasma, and photocatalytic oxidation), and biological (biofiltration, biotrickling, and bioscrubbing). Each technology is elucidated, and the performance in the removal of different pollutants is summarized. The application scopes, costs, operational stability, and secondary pollution of the technologies are compared. The generation of secondary pollution and long-term operation stability are issues that should be considered in future technological development. Lastly, a case analysis for engineering application is conducted.

Balancing the NH3 selective catalytic reduction (NH3-SCR) and catalytic oxidation performance is difficult but necessary for the synergistic elimination of NOx and chlorine-containing volatile organic compounds (CVOCs). We herein unveiled that electronic structure tailoring of the applied catalyst was an efficient pathway for balancing the catalytic behaviors in the NH3-SCR of NO and chlorobenzene catalytic oxidation (CBCO). Specifically, environmentally friendly CeO2 substituted by low valent Al3+ exhibited better NH3-SCR of NO and CBCO activity in comparison with the CeO2 sample without doping. Detailed characterizations and theoretical simulations revealed that the strong dopant-oxide pairs in the CeO2 with Al3+ doping significantly tailored the electronic structure of O 2p states, enhancing the amount of Lewis acid sites and promoting the ability of lattice oxygen to act as an oxidizing agent, thereby leading to superior performance for the synergistic elimination of NO/CB. The counterpart with substitution of high valent Ta5+ showed an opposite trend, due to that Ta5+ donated more electrons to the coordination oxygen than Ce4+ inhibiting lattice oxygen separating from the surface of the catalyst, and Lewis base sites were formed.

Co

Beaded activated carbons (BACs) were derived from waste bamboo tar through carbonization (500°C for 2 hr) followed by physical activation using carbon dioxide (800–900°C for 2–4 hr). The adsorbent was examined for their physical and chemical properties, adsorption capacities toward methylethylketone (MEK) and toluene, and regenerabilities under microwave heating. It was found that the maximum total surface area reached for bamboo-tar-derived BAC after physical activation was 1364 m2 g−1, and more than 95% of the area was attributed to the microporous structures. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were applied to the adsorption isotherm fitting, and the minimum R2 for each model was 0.986, 0.915, and 0.943, respectively. The isosteric heats of adsorption calculated based on D-R parameters for methylethylketone and toluene were 44.04 to 51.50 and 45.88 to 73.27 KJ mol−1, respectively. They were slightly over the range of physisorption and increased with adsorbate loading, which might be related to the micropore filling mechanism. Microwave regeneration under 600 W of power output removed most of the adsorbate (>93.03%) within 8 min. The results of this study are intended to benefit future study on waste-derived adsorbent in environmental applications. Recycling waste bamboo tar for the novel adsorbent preparation is shown feasible in this study. Beaded activated carbon (BAC) synthesized from this waste bamboo tar possessed a high specific surface area, which aided in the capturing of volatile organic compounds (VOCs). Three adsorption isotherms, Langmuir, Freundlich, Dubinin-Radushkevich (D-R) models can be applied in interpreting the experimental adsorption data, providing information on adsorption heat and possible adsorption mechanism. A potential microwave regeneration method for BAC is tested, showing high desorption efficiencies with minimum heel formation. These findings can provide a new pathway for waste bamboo tar management and VOC abatement using adsorbents.

Volatile organic compounds (VOCs) exists ubiquitously in chemical industries and were regarded as major contributors to air pollution, which should be strictly regulated. Vacuum ultraviolet irradiation coupled with photocatalytic oxidation (VUV-PCO) has been considered as an efficient approach to VOCs removal due to high-energy photons which could break down VOCs directly and be absorbed by photocatalysts to generate free radicals for further oxidation. However, the photochemical transformation mechanisms of VOCs have not been fully revealed. Herein, we systematically analyzed the intermediates using proton-transfer-reaction mass spectrometer (PTR-MS) to explore the transformation mechanisms of toluene degradation in VUV and VUV-PCO processes. VUV-PCO process displayed superior toluene degradation efficiency (50 %) and mineralization efficiency (65 %) compared with single VUV photolysis (35 %) and UV photocatalysis (5 %). TiO2 was deeply involved into CO2 generalization by amplifying the advantages of VUV system and further mineralizing the intermediates. In VUV and VUV-PCO processes, O2 participation changed the intermediates distribution by increasing multiple oxygenated products, while the introduction of water contributed to the formation and degradation of most intermediates. A possible degradation mechanism of toluene under VUV irradiation combined with TiO2 was proposed. This study provides a deep mechanistic insight into VOCs degradation by VUV-PCO process.