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Graphitic carbon nitride (g-C3N4) is considered a potential photoactive semiconductor for photocatalytic hydrogen evolution (PHE). Although being active in producing hydrogen, it is in general suffering from severe charge recombination rate, low mobility of charge and narrow visible light response range largely, which has restricted its greater application. Existing reviews on g-C3N4 are lacking of systematic and summative view on the effects of the physical-chemical structure-activity relationship between g-C3N4 and the modification involving phosphorus (P). Many studies indicate that adding P into g-C3N4 could effectively elevate the photo-activity. Underlying reasons for the observed improved photo-activity are discussed in this review. Here, P-containing g-C3N4 photocatalysts are grouped into the categories of P elemental doping, composite with elemental P, as well as the addition of metal phosphide as cocatalysts. These P-containing g-C3N4 possess novel properties demonstrating favorable photocatalytic activities as compared with the other elemental (such as O, S, B)-based materials. Therefore, in this mini review, we summarize and discuss the advances on the P-containing g-C3N4 photocatalysts, including the preparation strategies, physicochemical properties, the application for hydrogen production as well as the related reaction mechanism. Importantly, the physical-chemical structure-activity relationship between g-C3N4 and the integrated P is revealed. Finally, an overview of the current research status and challenges on future is presented, which would be helpful in designing and developing other P-containing photocatalysts for various photocatalytic applications.

Three-dimensionally ordered macroporous (3DOM) MnCo2O4-supported Co3O4 and AuPd (xAuPdz/yCo3O4/3DOM MnCo2O4; x = 0.56–1.98 wt%, z = 1.9–2.1, and y = 4.80–24.36 wt%) catalysts were prepared using polymethyl methacrylate (PMMA) microsphere-templating, incipient wetness impregnation, and polyvinyl alcohol (PVA)-protected reduction methods. Physicochemical properties of the materials were characterized by means of numerous techniques, and their catalytic activities were evaluated for methane combustion. It is found that the xAuPdz/yCo3O4/3DOM MnCo2O4 samples with a surface area of 26.5–53.1 m2/g possessed a high-quality 3DOM architecture, in which the AuPd nanoparticles (NPs) with a size of 4.6–5.8 nm were highly dispersed on the surface of the macropore framework. Among all of the samples, 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 exhibited the highest catalytic activity: the T10%, T50%, and T90% (temperatures required for achieving methane conversions of 10, 50, and 90 %, respectively) were 262, 340, and 408 °C at a space velocity of 40,000 mL/(g h). Partial deactivation of the 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 sample due to introduction of water vapor or carbon dioxide was reversible. It is concluded that the good catalytic performance of 1.98AuPd2.1/18.20Co3O4/3DOM MnCo2O4 was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Co3O4 or AuPd2.1 NPs and 3DOM MnCo2O4.

SnO2 is widely used in catalysis owing to its oxygen vacancies, reducible oxygen species, and acidity. In this work, Ru nanoparticles (NPs) supported on three-dimensionally ordered macroporous (3DOM) SnO2 (xRu/3DOM SnO2, Ru loading (x) = 0.09–1.65 wt%) were fabricated via the polyvinyl alcohol-protected reduction routes, and their catalytic activities were determined for trichloroethylene (TCE) and/or toluene oxidation. It was shown that the 0.98Ru/3DOM SnO2 sample exhibited the best activity and good thermal stability, with the temperature (T90% ) and apparent activation energy at a TCE (1000 ppmv) conversion of 90% being 300 °C and 44 kJ/mol at space velocity = 40,000 mL/(g h), respectively. Trichloromethane, carbon tetrachloride , tetrachloroethylene, and trichloroacetaldehyde hydrate were the main intermediates in TCE oxidation. The high catalytic performance of 0.98Ru/3DOM SnO 2 was attributed to the presence of hydroxyl groups adsorbed at the oxygen vacancies, strong O2 adsorption ability, good low-temperature reducibility, and strong interaction between Ru NPs and 3DOM SnO2. In addition, a catalytic mechanism over xRu/3DOM SnO2 was proposed under dry and humid conditions. The introduction of H2O could block some of the reaction pathways from inhibiting the production of C2Cl4, reduce formation of some by-products (e.g., CH2Cl2, CH3COOH, and C2H2Cl2), promote removal of the chlorine species, and generate a greater amount of HCl and a smaller amount of Cl2. Furthermore, introducing toluene into the TCE stream could generate smaller amounts of organic chlorine by-products and greater amounts of inorganic chlorine products (HCl and Cl2 ). We are sure that this work can provide a guideline for the industrial application of supported Ru catalysts in the removal of Cl-containing volatile organic compounds .

The thermocatalytic decomposition (TCD) of methane is considered as a milestone towards the production of valuable COx-free hydrogen and carbon nanomaterials without the use of steam or O2. Previous reviews have been aimed at methane decomposition over the different catalysts, such as nickel-based catalysts, non-nickel-based catalysts, metal oxide-supported catalysts, and carbon-supported catalysts. The Ni-based catalysts are suitably applied for methane TCD process due to their high activity and low cost. However, the loss of activity and/or stability with reaction time is one of the most notable challenges in the use of Ni-based catalysts, and a number of studies on the roles of various factors in overcoming such a problem can be found in the literature. Recently, the use of the second metal as a promoter to control catalyst deactivation has attracted much attention. The present review focuses on classification of the different promoters based on the periodic table of elements, such as alkali metals, alkaline earth, transition metals, noble metals, and rare earth metals, and makes a detailed discussion on promotional roles in influencing their physicochemical properties and catalytic performance of the Ni-based catalysts. The generalized structure-performance relationship of the metals-doped catalysts may give an appreciated reference to the design of catalysts with highly pure hydrogen production and carbon nanomaterials. In addition, this review also covers the works on effects of the promoters on nature and morphology of the formed carbon nanomaterials. The use of transition metals (Fe, Co or Cu), noble metal (Pd or Pt), and rare earth metal (La) with a suitable loading as a promoter influenced performance and lifespan of the catalyst and the interaction of Ni particles with the support. Among these promoters, Cu, Pd, La, and Cu–Pd as a dopant have demonstrated superior performance, which was attributed to the capability of these elements in prohibiting carbon accumulation on the active Ni components.

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.

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.

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.

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.

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.

Herein we fabricated the supported single-atom silver catalysts using an in situ molten salt method. The Mn2O3 nanowires supported single-atom silver catalyst (i.e., 0.06 wt% Ag/Mn2O3) exhibited excellent catalytic activity for toluene combustion, with the temperatures required for 50 and 90% of toluene conversions being 170 and 205 °C, respectively, at a space velocity of 40,000 mL/(g h). However, the toluene conversion at 205 °C quickly decreased from 90 to 30% within 2.5 h of on-stream reaction. Based on the various characterization results, we found that there were no aggregation of Ag particles, no change in crystal structure of the Mn2O3 nanowire support, and no carbon deposition on the catalyst surface, and the quick deactivation of 0.06 wt% Ag/Mn2O3 was mainly associated with the low oxygen activation ability. The proper CeO2 addition to the 0.06 wt% Ag/Mn2O3 catalyst was found to not only improve the catalytic activity but also significantly enhance the stability of the catalyst. Toluene conversion at 195 °C over 0.63 wt% CeO2-0.06 wt% Ag/Mn2O3 decreased by only 10% in 50 h of on-stream reaction. Because Ag and CeO2 particles were highly dispersed on the Mn2O3 nanowire support, the oxygen species formed at the surface oxygen vacancies of CeO2 could efficiently migrate to the active sites (i.e., the interface of Ag-Mn2O3) and replenish the surface reactive lattice oxygen species. Thus, the present single-atom silver catalyst is an alternative for commercial noble metal catalysts for the removal of VOCs. Keywords: Volatile organic compounds, Catalytic oxidation, Single-atom silver catalyst, In-situ molten salt method

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.

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.

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.

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.

The Pd-based catalysts have been widely studied for the combustion of volatile organic compounds, in which the roles of the Pd and the support are still not known clearly. In this study, mesoporous Co3O4 and CoO (i.e., meso-Co3O4 and meso-CoO) were prepared and used as support for the loading of Pd nanoparticles (NPs). The supported Pd samples performed much better than the supports for o-xylene combustion, in which the Pd/meso-CoO sample showed the best catalytic activity (T90% = 173 °C), giving rise to reaction rates at 170 °C 3.5 and 84 times higher than those over the Pd/meso-Co3O4 and meso-CoO samples, respectively. It has been established that the meso-CoO sample possessed strong ability to activate oxygen molecules to the active oxygen species, the loaded Pd NPs in a metallic Pd phase was beneficial for o-xylene adsorption, and the adsorbed o-xylene species could immediately react with the active oxygen species at the interface between Pd NPs and meso-CoO. Therefore, we conclude that the excellent catalytic performance of the Pd/meso-CoO sample was associated with its highly active Pd–CoO interface.

Mesoporous cubic PdxPt (x = 0.43–8.52) alloys with surface areas of 26–32 m2/g were synthesized using the KIT-6-templating method. Physicochemical properties of the materials were characterized by means of various techniques, and their catalytic activities were evaluated for methane combustion. It is found that the Pd and Pt were uniformly distributed in the PdxPt alloys. The addition of Pt to Pd exerted a significant effect on the redox property of Pd. The PdxPt alloys possessed a higher methane activation ability than the monometallic Pd. The oxidized Pd–Pt (i.e., PdO–PtO2) were more active than the metallic Pd0–Pt0. The Pd2.41Pt sample performed the best for methane combustion (T10%, T50%, and T90% were 272, 303, and 322 °C at SV = 100,000 mL/(g h); TOFPd, TOFPt, TOFPd + Pt, and specific reaction rate at 280 °C were 0.85 × 10−3 s−1, 1.98 × 10−3 s−1, 0.59 × 10−3 s−1, and 4.46 μmol/(gcat s), respectively). The deactivation of the Pd2.41Pt sample induced by 2.5–5.0 vol% CO2 or H2O addition was reversible, but its deactivation due to 100 ppm SO2 introduction was irreversible. It is concluded that the excellent catalytic performance of the Pd2.41Pt sample was associated with its good mesoporous structure, Pd–Pt alloy and PdO–PtO2 coexistence, and good methane and oxygen activation ability.

In this work, we first used the oil-phase co-reduction strategy to synthesize the RuxMny (Mn/Ru molar ratio (y/x) = 7 : 20, 21 : 25, and 17 : 10) intermetallic compounds, then used the KIT-6-templeting method to prepare mesoporous titania (meso-TiO2), and finally used the impregnation method to generate the RuxMny/meso-TiO2 (Ru loading = 0.60–0.79 wt%) catalysts. Various techniques were used to measure physicochemical properties of the samples, and their catalytic performance was determined for methyl ethyl ketone (MEK) oxidation. It is found that the RuxMny/meso-TiO2 samples possessed a three-dimensionally ordered mesoporous structure, a surface area of 71–173 m2/g, and a uniform RuxMny particle size of 2.3–2.9 nm. Among all of the samples, Ru25Mn21/meso-TiO2 exhibited the best catalytic performance and good hydrothermal stability: the temperatures at MEK conversions of 10, 50, and 90 % were 131, 226, and 248 °C at a space velocity of 20,000 mL/(g h), with the apparent activation energy, specific reaction rate at 160 °C, and turnover frequency (TOF) at 160 °C being 73 kJ/mol, 41.73 mmol/(gRu s), and 4.20 s−1, respectively. In addition, introduction of 5 vol% moisture to the reaction system exerted a positive effect on catalytic activity of Ru/meso-TiO2 or Ru25Mn21/meso-TiO2 at higher temperatures. Such good performance of the Ru25Mn21/meso-TiO2 sample was related to its well dispersed Ru25Mn21 nanoparticles, high adsorbed oxygen species concentration, active surface lattice oxygen, high MEK adsorption capacity, good redox ability, and strong interaction between Ru25Mn21 and meso-TiO2. We propose that MEK might be oxidized by the adsorbed oxygen and/or surface lattice oxygen species via in turn formation of 2,3-butanedione, acetaldehyde, acetic acid, formaldehyde, and formic acid, all of which were finally converted to water and carbon dioxide.

The design and synthesis of g-C3N4 with favourable physical-chemical architecture are important factors in influencing its photoactivity. Herein, a phosphorus (P) vapor assisted synthetic strategy was employed to fabricate the P-doped hollow g-C3N4 photocatalysts with ultrathin shell structure (

The low-cost and environmentally benign elemental red phosphorus (RP) is a new class of photocatalysts with tunable bandgaps (ca. 1.5–2.4 eV) and has a strong visible-light response. It has been considered as a promising metal-free photocatalyst for solving the energy crisis and environmental problems. Unfortunately, due to the low-charge carrier mobility, and serve charge trapping effects, its photocatalytic activity is still restricted in comparison with the traditional compound photocatalysts. Considerable efforts, such as morphology modification, cocatalysts addition, heterostructure construction, charge trapping mitigation, have been conducted to improve the photocatalytic activity of the RP photocatalysts. In this review, the physical and chemical properties and the synthetic strategies of the RP photocatalysts were summarized along with the application in environmental remediation accompanied by the photocatalytic reaction mechanism. Finally, an overview and outlook on the problems and future avenues in designing and constructing advanced RP photocatalysts were also proposed.

Cobalt oxide is a typical transition metal oxide that exhibits high catalytic activity for the total oxidation of volatile organic compounds. In this study, a reduction process in a glycerol solution was adopted to generate mesoporous CoO (meso-CoO) or CoO x (meso-CoO x ) from mesoporous Co 3 O 4 (meso-Co 3 O 4 ). The obtained samples were rich in Co 2+ species and exhibited high catalytic activity for o -xylene oxidation. The meso-CoO x sample with the largest surface Co 2+ amount performed the best: The o -xylene conversion at 240 °C was 83%, and the reaction rate over meso-CoO x was nine times higher than that over meso-Co 3 O 4 . It is found that the samples with more surface Co 2+ species possessed better oxygen activation ability, and the Co 2+ species were the active sites that favored the formation of highly active O 2 − and O 2 2− (especially O 2 − ) species.

Palladium-based catalysts are highly active for eliminating volatile organic compounds. Reducing the use of noble metals and enhancing performance of a catalyst are always desirable. The three-dimensionally ordered macroporous (3DOM) Mn2O3-supported transition metal M (M = Mn, Cr, Fe, and Co)-doped Au–Pd nanoparticles (NPs) with an Au–Pd–xM loading of 1.86–1.97 wt% were prepared using the modified polyvinyl alcohol-protected reduction method. It is found that the Au–Pd–xM NPs with a size of 3.6–4.4 nm were highly dispersed on the surface of 3DOM Mn2O3. The 1.94 wt% Au–Pd–0.21Co/3DOM Mn2O3 and 1.94 wt% Au–Pd–0.22Fe/3DOM Mn2O3 samples performed the best for the oxidation of methane and o-xylene, respectively. The methane oxidation rate at 340 °C (339.0 × 10−6 mol/(gPd s)) over 1.94 wt% Au–Pd–0.21Co/3DOM Mn2O3 was three times higher than that (93.8 × 10−6 mol/(gPd s)) over 1.97 wt% Au–Pd/3DOM Mn2O3, and the o-xylene reaction rate at 140 °C (2.59 μmol/(gN s) over 1.94 wt% Au–Pd–0.22Fe/3DOM Mn2O3 was two times higher than that (0.93 μmol/(gN s) over 1.97 wt% Au–Pd/3DOM Mn2O3. It is concluded that doping a certain amount of the transition metal to Au–Pd/3DOM Mn2O3 could modify the microstructure of the alloy NPs, thus improving the oxygen activation and methane adsorption ability. We are sure that the M-doped Au–Pd/3DOM Mn2O3 materials are promising catalysts for the efficient removal of volatile organic compounds.

Three-dimensionally ordered macroporous La 0.6 Sr 0.4 CoO 3 (3DOM LSCO) and its supported gold and manganese oxide ( y Mn 3 O 4 - z Au/3DOM LSCO; y = 0.75–2.50 wt%, z = ca. 2.0 wt%) nanoparticles (NPs) were prepared using the polymethyl methacrylate-templating, polyvinyl alcohol-protected reduction, and physical adsorption methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is shown that the 3DOM LSCO in y Mn 3 O 4 - z Au/3DOM LSCO with a surface area of 20–24 m 2 /g displayed a rhombohedral crystal structure, and Mn 3 O 4 (size: 5–12 nm) and Au (size: 3–4 nm) NPs were highly dispersed on the surface of 3DOM LSCO. There were good correlations of adsorbed oxygen species concentration and low-temperature reducibility with catalytic activity of the sample. The 1.67Mn 3 O 4 -2Au/3DOM LSCO sample performed the best, giving the T 50% and T 90% (temperatures required for achieving toluene conversions of 50 and 90%) of 214 and 230 °C at a space velocity of 20,000 mL/(g h), respectively. The introduction of water vapor to the reaction system caused a partial deactivation of the 1.67Mn 3 O 4 -2Au/3DOM LSCO sample, and such a deactivation was reversible. The apparent activation energies (41.7–47.4 kJ/mol) obtained over y Mn 3 O 4 -2Au/3DOM LSCO were lower than those (49.2–56.8 kJ/mol) obtained over 3DOM LSCO, 2Au/3DOM LSCO, and 1.56Mn 3 O 4 -2Au/Bulk LSCO. It is concluded that the large surface area, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au or Mn 3 O 4 NPs and 3DOM LSCO were responsible for the good catalytic performance of 1.67Mn 3 O 4 -2Au/3DOM LSCO.

Three-dimensionally ordered macroporous CoCr2O4 (3DOM CoCr2O4) and its supported Au–Pd alloy (xAuPdy/3DOM CoCr2O4; x = 0.98 and 1.93 wt%; Pd/Au molar ratio (y) = 1.93–1.96) nanocatalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of a number of techniques, and their catalytic activities were evaluated for methane combustion. The 3DOM CoCr2O4 and xAuPdy/3DOM CoCr2O4 samples possessed a high-quality 3DOM structure and a surface area of 33–36 m2/g. The Au–Pd alloy nanoparticles (NPs) with an average size of 3.3 nm were uniformly dispersed on the surface of the samples. The 1.93AuPd1.95/3DOM CoCr2O4 sample showed the best catalytic performance: the T10%, T50%, and T90% (temperatures required for achieving methane conversion of 10, 50, and 90%, respectively) were 305, 353, and 394 °C at a space velocity (SV) of 20,000 mL/(g h). The effects of SV, water vapor, and sulfur dioxide on the catalytic activity of the 1.93AuPd1.95/3DOM CoCr2O4 sample were also examined. It is concluded that the excellent catalytic performance of 1.93AuPd1.95/3DOM CoCr2O4 was associated with the higher surface area and adsorbed oxygen species concentration, better low-temperature reducibility, and strong interaction between Au–Pd alloy NPs and 3DOM CoCr2O4.

Using the molten salt and polyvinyl alcohol-protected reduction method, we fabricated Co 3 O 4 octahedron-supported Au-Pd ( x (AuPd y )/Co 3 O 4 ; x = (0.18, 0.47, and 0.96) wt%; y (Pd/Au molar ratio) = 1.85−1.97) nanocatalysts. The molten salt-derived Co 3 O 4 sample possessed well-defined octahedral morphology, with an edge length of 300 nm. The Au-Pd nanoparticles, with sizes of 2.7−3.2 nm, were uniformly dispersed on the surface of Co 3 O 4 . The 0.96 (AuPd 1.92 )/Co 3 O 4 sample showed the highest catalytic activity for toluene and o -xylene oxidation, and the temperature required for achieving 90% conversion of toluene and o -xylene was 180 and 187 °C, respectively, at a space velocity of 40000 mL/(g–h). The high catalytic performance of Co 3 O 4 octahedron-supported Au-Pd nanocatalysts was associated with the interaction between Au-Pd nanoparticles and Co 3 O 4 and high concentration of adsorbed oxygen species.

Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87&ndash, 0.91 wt%, y = 0.51&ndash, 1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49&ndash, 53 m2/g. The noble metal nanoparticles (NPs) with a size of 3&ndash, 4 nm were uniformly dispersed on the surface of 3DOM TiO2. The 0.91Au0.51Pd/3DOM TiO2 sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 &deg, C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au0.51Pd/3DOM TiO2 sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H2O introduction of 0.91Au0.51Pd/3DOM TiO2 was reversible, while that induced by CO2 addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au0.51Pd/3DOM TiO2. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au0.51Pd/3DOM TiO2 sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO2 as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au0.51Pd/3DOM TiO2. We believe that 0.91Au0.51Pd/3DOM TiO2 may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics.

Catalytic oxidation is one of the effective pathways for completely eliminating volatile organic compounds (VOCs) emitted from industrial and transportation activities. Meanwhile, single-atom catalysts have excellent application prospects in numerous reactions due to their high metal atomic utilization efficiency. In this work, we adopted a novel strategy to prepare an active Pd/Co single-atom catalyst (i.e., Pd1Co1/Al2O3) for benzene oxidation. The successful formation of the atomically dispersed palladium and cobalt species on Al2O3 was verified by the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure. By the in situ temperature-programmed techniques and in situ diffuse reflectance Fourier transform infrared spectroscopy, we observed a double effect of the palladium and cobalt oxide active sites, resulting in an enhanced performance for benzene oxidation. A benzene conversion of 90 % was achieved over the Pd1Co1/Al2O3 catalyst at 250 °C and a space velocity of 40,000 mL/(g h). Interestingly, the catalyst also possessed enhanced sulfur resistance performance. The good regeneration ability of the active sites in the catalyst was due to the single-atom dispersion of Pd and Co. In addition, we deduce that benzene oxidation might occur over Pd1Co1/Al2O3 via a pathway of benzene → cyclohexadiene → phenol → quinone → maleate → acetate → CO2 and H2O. We believe that the obtained results can provide a useful idea for rationally designing the double active site single-atom catalysts and understanding the mechanism of VOCs oxidation.

Three-dimensionally ordered macro-/mesoporous alumina (3DOM Al2O3)-supported cobalt oxide and platinum nanocatalysts (xPt/yCo3O4/3DOM Al2O3, Pt mass fraction (x%) = 0−1.4%, Co3O4 mass fraction (y%) = 0−9.2%) were prepared using poly(methyl methacrylate) templating, incipient wetness impregnation and polyvinyl alcohol-protected reduction. The resulting xPt/yCo3O4/3DOM Al2O3 samples displayed a high-quality 3DOM architecture with macropores (180–200 nm in diameter) and mesopores (4–6 nm in diameter) together with surface areas in the range of 94 to 102 m2/g. Using these techniques, Co3O4 nanoparticles (NPs, 18.3 nm) were loaded on the 3DOM Al2O3 surface, after which Pt NPs (2.3–2.5 nm) were uniformly dispersed on the yCo3O4/3DOM Al2O3. The 1.3Pt/8.9Co3O4/3DOM Al2O3 exhibited the best performance for toluene oxidation, with a T90% value (the temperature required to achieve 90% toluene conversion) of 160 °C at a space velocity of 20000 mL g−1 h−1. It is concluded that the excellent catalytic performance of the 1.3Pt/8.9Co3O4/3DOM Al2O3 is owing to well-dispersed Pt NPs, the high concentration of adsorbed oxygen species, good low-temperature reducibility, and strong interaction between the Pt and Co3O4 NPs, as well as the unique bimodal porous structure of the support.

In this review, we summarize the recent research progress on the preparation and catalytic performance of meso- and macroporous metal oxide or mixed metal oxide (including manganese oxides, cobalt oxides, iron oxides, chromium oxides, and perovskite-type oxides) catalysts and their supported transition metal and noble metal catalysts for the oxidative removal of typical volatile organic compounds (VOCs), which were prepared using the hard-templating and polyvinyl alcohol-protected reduction methods, respectively. Most of these porous catalysts performed well for the addressed reactions, which was associated with their surface areas, adsorbed oxygen species concentrations, low-temperature reducibility, interactions between noble metal or metal oxide and support as well as porous structures. In addition, the perspectives for developing high-performance catalytic materials and novel VOCs removal technologies are also proposed.

Three-dimensionally ordered macroporous (3DOM) photocatalysts BiVO4 (denoted as 3D-BiV), AgBr/3D-BiV, and 0.17 wt% M/AgBr/3D-BiV (M Au, Pt, and Pd) were prepared using the polymethyl methacrylate-templating, low-temperature deposition, and polyvinyl alcohol-protected reduction methods, respectively. The as-prepared BiVO4 possessed a good-quality 3DOM structure and a high surface area. It is found that the AgBr and noble metals were uniformly distributed on the surface of 3D-BiV. Among the M/AgBr/3D-BiV samples, the 0.17 wt% Pd/AgBr/3D-BiV sample showed the highest photocatalytic activity for the degradation of 4-chlorophenol (4-CP) under visible light illumination (i.e., complete 4-CP degradation could be achieved within 150 min), which was associated with its good 3DOM structure, high surface oxygen adspecies concentration, easy transfer and separation of photogenerated carriers, and synergistic effect between AgBr or Pd nanoclusters and BiVO4.

Three-dimensionally ordered macroporous (3DOM) praseodymium oxide and terbium oxide with mesoporous walls and cubic crystal structures have been successfully fabricated with polymethyl methacrylate (PMMA) as hard template and F127, sucrose, and l -lysine as surfactant. Physicochemical properties of the materials were characterized by means of numerous techniques. It is shown that the Pr6O11 and Tb4O7 samples displayed a 3DOM architecture with polycrystalline wormhole-like mesoporous walls. The nature of surfactant and solvent and calcination condition had important effects on the pore structure and surface area of the final product. The introduction of surfactant and the partial carbonization of sucrose or l -lysine favored the enhancement in surface area of the 3DOM-structured materials, with the 3DOM Pr6O11 and Tb4O7 samples derived with F127 showing the highest surface areas of 32.0 and 25.2 m2/g, respectively. The low-temperature reducibility of the Pr6O11 and Tb4O7 samples decreased according to the sequences of Pr6O11-F127 > Pr6O11-Sucrose > Pr6O11-Lysine and Tb4O7-F127 > Tb4O7-Sucrose > Tb4O7-Lysine, coinciding with the order in surface oxygen vacancy density. The improved physicochemical properties associated with the generation of 3DOM skeletons and wormhole-like mesoporous walls rendered the Pr6O11-F127 and Tb4O7-F127 samples to perform the best in the oxidation of CO.

The polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction routes were adopted to prepared three-dimensionally ordered macroporous (3DOM) Co 3 O 4 and its supported gold–palladium alloy ( x AuPd/3DOM Co 3 O 4 , x = 0.50–1.99 wt% and Au/Pd mass ratio = 1:1) nanocatalysts. The 3DOM Co 3 O 4 supported Au–Pd samples performed much better than supported single Au or Pd samples, with the 1.99AuPd/3DOM Co 3 O 4 sample showing the best performance: the T 10% , T 50% , and T 90% (temperatures required for achieving toluene conversions of 10%, 50%, and 90%) were 145, 164, and 168 °C at a space velocity of 40,000 mL/(g h), respectively. The 3DOM Co 3 O 4 supported Au–Pd nanocatalysts also exhibited better catalytic stability and more moisture-tolerant ability than the supported Au or Pd samples for toluene oxidation. The apparent activation energies (33–41 kJ/mol) over x AuPd/3DOM Co 3 O 4 were much lower than those (52–112 kJ/mol) over 3DOM Co 3 O 4 and supported single Au or Pd samples, with the 1.99AuPd/3DOM Co 3 O 4 sample exhibiting the lowest apparent activation energy (33 kJ/mol). It is concluded that better oxygen activation ability and stronger noble metal–3DOM Co 3 O 4 interaction were responsible for the excellent catalytic performance of 1.99AuPd/3DOM Co 3 O 4 .

To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au–Pd alloy nanoparticles (NPs) to generate high-performance Au–Pd–xCoO/three-dimensionally ordered macroporous (3DOM) Co3O4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO–CoO active sites, which was beneficial for the improvement in adsorption and activation of CH4 and catalytic performance. The Au–Pd–0.40CoO/3DOM Co3O4 sample performed the best (T90% = 341 °C at a space velocity of 20 000 mL g–1 h–1). Deactivation of the 3DOM Co3O4-supported Au–Pd, Pd–CoO, and Au–Pd–xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd–CoO/3DOM Co3O4 catalyst at high temperatures (680–800 °C) might be due to decomposition of the PdOy active phase into aggregated Pd0 NPs. The Au–Pd–xCoO/3DOM Co3O4 nanocatalysts exhibi...

Three-dimensionally macroporous perovskite-type oxides EuFeO 3 (EFO-3DOM, EFO-sucrose-1, EFO-sucrose-2, and EFO-sucrose-3, respectively) have been prepared using the polymethyl methacrylate-templating method in the absence or presence of sucrose. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the total oxidation of toluene. It is shown that all of the EFO samples were of single-phase orthorhombic crystal structure with a 3DOM architecture. The sucrose addition during the preparation process had a great effect on the surface area and porous structure of the final product. A clear correlation of surface area, surface oxygen species concentration, and low-temperature reducibility with the catalytic performance was observed. The EFO-sucrose-1 catalyst performed the best, giving the T 50% and T 90% of 312 and 347 °C at space velocity = 20,000 mL/(g h), respectively. The apparent activation energies of the 3DOM-structured EFO samples were in the range of 82–97 kJ/mol. It is concluded that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility account for the good catalytic activity of EFO-sucrose-1.

Three-dimensionally ordered mesoporous Co3O4 (meso-Co3O4) and its supported gold (xAu/meso-Co3O4, x = 3.7–9.0 wt%) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected colloidal deposition methods, respectively. The meso-Co3O4 and xAu/meso-Co3O4 samples exhibited a high surface area of 91–94 m2/g. The Au nanoparticles with a size of 1–5 nm were uniformly deposited inside the mesoporous channels of meso-Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO or BTX (benzene, toluene, and o-xylene) oxidation. Among meso-Co3O4 and xAu/meso-Co3O4, the 6.5Au/meso-Co3O4 sample performed the best, giving the T90% (the temperature required for achieving a CO or BTX conversion of 90%) of −45, 189, 138, and 162 °C for the oxidation of CO, benzene, toluene, and o-xylene, respectively. The apparent activation energies (23 and 45–55 kJ/mol) over 6.5Au/meso-Co3O4 were much lower than those (48 and 72–92 kJ/mol) over bulk Co3O4 for CO and BTX oxidation, respectively. The effects of water vapor, carbon dioxide, and sulfur dioxide on the catalytic activity of the 6.5Au/meso-Co3O4 sample were also examined. It is concluded that the higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and meso-Co3O4 were responsible for the excellent catalytic performance of 6.5Au/meso-Co3O4.

The three-dimensionally ordered macroporous (3DOM) CeO2-supported Au–Pd alloys (xAuPdy/3DOM CeO2, x is the total loading (wt%) of Au and Pd, and y is the Pd/Au molar ratio) were synthesized using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The samples were characterized by a number of analytical techniques, and their catalytic performance was evaluated for the combustion of trichloroethylene (TCE). It is found that the xAuPdy/3DOM CeO2 samples displayed a good-quality 3DOM architecture, and the noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the skeleton surface of 3DOM CeO2. Among all of the samples, 2.85AuPd1.87/3DOM CeO2 exhibited the highest catalytic activity, with the temperature at a TCE conversion of 90% (T90%) being 415 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 2.85AuPd1.87/3DOM CeO2 sample possessed the lowest apparent activation energy (33 kJ/mol), excellent catalytic stability, and good moisture- and chlorine-tolerant behaviors. Alloying of Au with Pd changed the pathway of TCE oxidation and reduced formation of perchloroethylene. We conclude that the excellent catalytic performance for TCE combustion of 2.85AuPd1.87/3DOM CeO2 was associated with the highly dispersed AuPd1.87 alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd1.87 NPs and 3DOM CeO2 as well as the high-quality 3DOM structure and high surface acidity.

Three-dimensionally ordered macroporous (3DOM) La 0.6 Sr 0.4 MnO 3 (LSMO) and its supported gold ( x Au/LSMO, x = 3.4–7.9 wt%) catalysts were prepared using the polymethyl methacrylate-templating and gas-bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. There were good correlations of surface-adsorbed oxygen species concentration and low-temperature reducibility with the catalytic activity of the sample for CO and toluene oxidation. Among the LSMO and x Au/LSMO samples, 6.4Au/LSMO performed the best, giving T 50% and T 90% values of −19 and 3 °C for CO oxidation and 150 and 170 °C for toluene oxidation, respectively. The apparent activation energies (31–32 and 44–48 kJ/mol) obtained over x Au/LSMO were much lower than those (45 and 59 kJ/mol) obtained over LSMO for the oxidation of CO and toluene, respectively. It is concluded that higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and LSMO are responsible for the excellent catalytic performance of 6.4Au/LSMO.

Porous monoclinic bismuth vanadate (BiVO(subscript 4-δ)) and sulfur‐doped bismuth vanadates (BiVO(subscript 4-δ)S(subscript 0.05), BiVO(subscript 4-δ)S(subscript 0.08), and BiVO(subscript 4-δ)S(subscript 0.12)) were synthesized by a dodecylamine‐assisted alcohol‐hydrothermal route in the absence and presence of thiourea or Na2S. The physicochemical properties of the materials were characterized and their photocatalytic performance for the degradation of methylene blue and formaldehyde under visible light was evaluated. The samples have a single phase monoclinic scheetlite crystal structure with a porous olive‐like morphology, surface areas of 8.4-12.5 m^2/g, and bandgap energies of 2.40-2.48 eV. Surface Bi^(5+), Bi^(3+), V^(5+), and V^(4+) species were present on the S‐doped BiVO(subscript 4-δ) samples. Sulfur doping influenced the surface Bi^(5+)/Bi^(3+), V^(5+)/V^(4+), and Oads/Olatt molar ratios, and the amount of sulfur doped had an important effect on the photocatalytic performance. Under visible light, BiVO(subscript 4-δ)S(subscript 0.08) performed the best in the photodegradation of methylene blue and formaldehyde. A higher surface oxygen species concentration and a lower bandgap energy were responsible for the excellent visible light photocatalytic performance of BiVO(subscript 4-δ)S(subscript 0.08).

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) LaMnO3 supported MnOx (5, 8, 12, 16 wt% MnOx/3DOM LaMnO3) catalysts were prepared using the in situ tryptophan-assisted poly(methyl methacrylate)-templating strategy. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the combustion of toluene and methanol. It is shown that the MnOx/3DOM LaMnO3 samples displayed a 3DOM architecture and a high surface area of 19–31 m2/g. The 12 wt% MnOx/3DOM LaMnO3 sample showed the highest oxygen adspecies concentration and the best low-temperature reducibility as well as the highly dispersed MnOx particles on the LaMnO3 surface, giving the highest TOF values of 7.9 x 10−6 s−1 for toluene combustion at 160 °C and 7.3 x 10−6 s−1 for methanol combustion at 80 °C. The apparent activation energies of the MnOx/3DOM LaMnO3 catalysts were 61–62 and 48–54 kJ/mol for toluene and methanol combustion, respectively. It is concluded that the excellent catalytic performance of 12 wt% MnOx/3DOM LaMnO3 was associated with its highest oxygen adspecies concentration, best low-temperature reducibility, and strong interaction between MnOx and 3DOM LaMnO3.

Rhombohedrally crystallized chain-like LaMnO3 and its supported gold (xAu/LaMnO3; x = 1.4, 3.1, and 4.9 wt%) catalysts have been prepared using the poly(ethylene glycol)-assisted polymethyl methacrylate-templating and gas bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. It is shown that there were good correlations of surface adsorbed oxygen species concentration and low-temperature reducibility with catalytic activity of the samples for the oxidation of CO and toluene. Among the LaMnO3 and xAu/LaMnO3 samples, 4.9Au/LaMnO3 performed the best, giving the T50% and T90% of 61 and 91 °C for CO oxidation, and of 201 and 226 °C for toluene combustion, respectively. The apparent activation energies (29–50 and 47–62 kJ/mol) of the chain-like LaMnO3 and xAu/LaMnO3 samples were much smaller than those (63 and 97 kJ/mol) of the bulk LaMnO3 sample for the oxidation of CO and toluene, respectively. We believe that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility as well as the strong interaction between Au nanoparticles and chain-like LaMnO3 support might account for the high catalytic performance of 4.9Au/LaMnO3.

Uniform hollow spherical rhombohedral LaMO3 and solid spherical cubic MOx (M = Mn and Co) NPs were fabricated using the PMMA-templating strategy. Hollow spherical LaMO3 and solid spherical MOx NPs possessed surface areas of 21-33 and 21-24 m(2)/g, respectively. There were larger amounts of surface-adsorbed oxygen species and better low-temperature reducibility on/of the hollow spherical LaMO3 samples than on/of the solid spherical MOx samples. Hollow spherical LaMO3 and solid spherical MOx samples outperformed their nanosized counterparts for oxidation of CO and toluene, with the best catalytic activity being achieved over the solid spherical Co3O4 sample for CO oxidation (T50% = 81 °C and T90% = 109 °C) at space velocity = 10,000 mL/(g h) and the hollow spherical LaCoO3 sample for toluene oxidation (T50% = 220 °C and T90% = 237 °C) at space velocity = 20,000 mL/(g h). It is concluded that the higher surface areas and oxygen adspecies concentrations and better low-temperature reducibility are responsible for the excellent catalytic performance of the hollow spherical LaCoO3 and solid spherical Co3O4 NPs. We believe that the PMMA-templating strategy provides an effective route to prepare uniform perovskite-type oxide and transition-metal oxide NPs.

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) LaCoO3 and its supported Au (xAu/3DOM LaCoO3, x = 0–7.63 wt%) catalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene and CO. It is shown that the xAu/3DOM LaCoO3 samples displayed a 3DOM architecture and a high surface area of 24–29 m2/g. The 7.63Au/3DOM LaCoO3 sample exhibited the highest adsorbed oxygen species concentration and the best low-temperature reducibility, and hence the best catalytic performance. Over 7.63Au/3DOM LaCoO3, the T10%, T50%, and T90% (corresponding to the temperatures required for achieving a reactant conversion of 10%, 50%, and 90%) were 136, 188, and 202 °C for toluene oxidation at space velocity (SV) = 20,000 mL/(g h), and −61, −6, and 42 °C for CO oxidation at SV = 10,000 mL/(g h), respectively. Over xAu/3DOM LaCoO3, the apparent activation energies were 31.4–37.4 kJ/mol for toluene oxidation and 16.6–19.4 kJ/mol for CO oxidation. We believe that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au and 3DOM LaCoO3 might account for the excellent catalytic performance of 7.63Au/3DOM LaCoO3.

Porous S-doped bismuth vanadate with an olive-like morphology and its supported cobalt oxide ( y wt% CoO x /BiVO 4− δ S 0.08 , y = 0.1, 0.8, and 1.6) photocatalysts were fabricated using the dodecylamine-assisted alcohol-hydrothermal and incipient wetness impregnation methods, respectively. It is shown that the y wt% CoO x /BiVO 4− δ S 0.08 photocatalysts were single-phase with a monoclinic scheetlite structure, a porous olive-like morphology, a surface area of 8.8–9.2 m 2 /g, and a bandgap energy of 2.38–2.41 eV. There was the co-presence of surface Bi 5+ , Bi 3+ , V 5+ , V 3+ , Co 3+ , and Co 2+ species in y wt% CoO x /BiVO 4− δ S 0.08 . The 0.8 wt% CoO x /BiVO 4− δ S 0.08 sample performed the best for methylene blue degradation under visible-light illumination. The photocatalytic mechanism was also discussed. We believe that the sulfur and CoO x co-doping, higher oxygen adspecies concentration, and lower bandgap energy were responsible for the excellent visible-light-driven catalytic activity of 0.8 wt% CoO x /BiVO 4− δ S 0.08 .

Strontium ferrite (SFO) hollow spheres with or without porous shells were fabricated via a novel one-pot hydrothermal route with the assistance of glucose and/or ethylenediamine. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic performance was evaluated for the combustion of toluene. It is shown that the SFO samples possessed an orthorhombic structure and displayed a porous hollow spherical morphology with a surface area of 18–27 m 2 /g. The SFO sample (SFO-3) derived hydrothermally at 170 °C with a glucose/ethylenediamine volumetric ratio of 0.3/1.0 exhibited the highest surface area and oxygen adspecies concentration and the best low-temperature reducibility. Among the SFO samples, the SFO-3 sample showed the best catalytic activity for toluene combustion, and the T 10% , T 50% , and T 90% were ca. 145, 255, and 298 °C at a space velocity of 20,000 mL/(g h), respectively. It is concluded that the good catalytic performance of SFO-3 was associated with its surface oxygen species concentration and better low-temperature reducibility.