Three-dimensionally ordered macroporous La0.6Sr0.4MnO3 (3DOM LSMO) supported manganese oxide and gold (yAu/zMnOx/3DOM LSMO; y = 1.76–6.85 wt %; z = 8 wt % (weight percent of Mn2O3)) nanocatalysts were fabricated by means of in situ poly(methyl methacrylate)-templating and gas bubble-assisted poly(vinyl alcohol)-protected reduction methods. The 3DOM LSMO support possessed a rhombohedral crystal structure and a surface area of 22–25 m2/g. MnOx and Au nanoparticles (NPs) (3.2–3.8 nm) were well dispersed on the surface of 3DOM LSMO. Catalytic performance of the samples for toluene oxidation was found to be well related to their surface adsorbed oxygen species concentrations and low-temperature reducibility. Among the as-prepared samples, 5.92Au/8MnOx/3DOM LSMO performed the best at a space velocity of 20 000 mL/(g h): the T50% and T90% (corresponding to toluene conversion of 50 and 90%) were 205 and 220 °C, respectively. The apparent activation energies (52.8–68.5 kJ/mol) obtained over the yAu/8MnOx/3DOM LSMO samples were much smaller than those (79.3–89.5 kJ/mol) obtained over the bulk LSMO supported counterparts. We believe that the excellent catalytic performance of 5.92Au/8MnOx/3DOM LSMO might be ascribed to the large surface area, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au NPs or MnOx and 3DOM LSMO.

•3D mesoporous PdxPt alloys are synthesized via a KIT-6-templating route.•The Pd2.41Pt sample performs the best in methane combustion.•PdO–PtO2 is the main active site for methane combustion.•Pd2.41Pt shows good thermal stability and good resistance to CO2 and H2O.•Methane can be more readily activated over the PdxPt alloys than over the Pd.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.Mesoporous PdxPt (x = 0.43–8.52) alloys are synthesized via a KIT-6-templating route. The excellent catalytic performance of the Pd2.41Pt sample is associated with its mesoporous structure, Pd–Pt alloy and PdO–PtO2 coexistence, and good methane and oxygen activation ability.Download full-size image

•Ordered mesoporous Co3O4 (meso-Co3O4) is prepared via the KIT-6-templating route.•meso-CoO and meso-CoOx are fabricated from meso-Co3O4 via a reduction process.•meso-CoOx with the largest surface Co2+ amount performs best for o-xylene oxidation.•Surface Co2+ species are beneficial for oxygen activation.•Active oxygen species formed in the Co2+ sites are mainly O2− and/or O22−.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 CoOx (meso-CoOx) from mesoporous Co3O4 (meso-Co3O4). The obtained samples were rich in Co2+ species and exhibited high catalytic activity for o-xylene oxidation. The meso-CoOx sample with the largest surface Co2+ amount performed the best: The o-xylene conversion at 240 °C was 83%, and the reaction rate over meso-CoOx was nine times higher than that over meso-Co3O4. It is found that the samples with more surface Co2+ species possessed better oxygen activation ability, and the Co2+ species were the active sites that favored the formation of highly active O2− and O22− (especially O2−) species.Download high-res image (128KB)Download full-size image

•3DOM BiVO4 is fabricated via the polymethyl methacrylate-templating route.•Fe2O3/3DOM BiVO4 is prepared by the incipient wetness impregnation method.•0.97Fe2O3/3DOM BiVO4 possesses the highest Oads density.•Fe2O3-3DOM BiVO4 heterojunction inhibits recombination of charge carriers.•0.97Fe2O3/3DOM BiVO4 shows excellent activity and stability for 4-NP degradation.The three-dimensionally ordered macroporous (3DOM) BiVO4 and its supported iron oxide (xFe2O3/3DOM BiVO4, x = 0.18, 0.97, and 3.40 wt%) photocatalysts were prepared using the ascorbic acid-assisted polymethyl methacrylate-templating and incipient wetness impregnation methods, respectively. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their photocatalytic activities were evaluated for the degradation of 4-nitrophenol under visible light illumination. It is found that the BiVO4 possessed a high-quality 3DOM architecture with a monoclinic crystal phase, and the Fe2O3 was highly dispersed on the surface of 3DOM BiVO4. The xFe2O3/3DOM BiVO4 samples much outperformed the 3DOM BiVO4 sample, and 0.97Fe2O3/3DOM BiVO4 showed the best photocatalytic performance (98% 4-nitrophenol was degraded in the presence of 0.6 mL H2O2 within 30 min of visible light illumination) and excellent photocatalytic stability. The introduction of H2O2 to the reaction system could promote the photodegradation of 4-nitrophenol by providing the active OH species generated via the reaction of photoinduced electrons and H2O2. The pseudo-first-order reaction rate constants (0.0876–0.1295 min−1) obtained over xFe2O3/3DOM BiVO4 were much higher than those (0.0033–0.0395 min−1) obtained over 3DOM or Bulk BiVO4 and Fe2O3/Bulk BiVO4, with the 0.97Fe2O3/3DOM BiVO4 sample exhibiting the highest rate constant. The enhanced photocatalytic performance of 0.97Fe2O3/3DOM BiVO4 was associated with its unique porous architecture, high surface area, Fe2O3 − BiVO4 heterojunction, good light-harvesting ability, high adsorbed oxygen species concentration, and excellent separation efficiency of photogenerated electrons and holes as well as the photo-Fenton degradation process.0.97Fe2O3/3DOM BiVO4 exhibits excellent photocatalytic activity for 4-NP degradation, which is mainly associated with its unique porous structure, Fe2O3–BiVO4 heterojunction, and excellent separation efficiency of photoinduced electrons/holes as well as the photo-Fenton degradation process.Download high-res image (137KB)Download full-size image

•Au–Pd–xM (M = Mn, Cr, Fe, Co) particles are fabricated and well dispersed on the 3DOM Mn2O3 surface.•Au–Pd–0.21Co/3DOM Mn2O3 exhibits the best catalytic activity for CH4 oxidation.•Au–Pd–0.22Fe/3DOM Mn2O3 shows the best catalytic activity for o-xylene oxidation.•M doping can enhance the oxygen activation and methane adsorption ability.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.The transition metal M (M = Mn, Cr, Fe, and Co)-doped Au–Pd/3DOM Mn2O3 nanocatalysts show super catalytic performance for methane and o-xylene oxidation, which is attributed to the enhanced oxygen activation and methane adsorption ability.Download high-res image (298KB)Download full-size image

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 exhibited better thermal stability and water tolerance ability compared to the 3DOM Co3O4-supported Au–Pd and Pd–CoO nanocatalysts. We believe that the supported Au–Pd–xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

•Ordered mesoporous Cr2O3 (meso-Cr2O3) is fabricated via the KIT-6-templating route.•xAu1Pd2/meso-Cr2O3 are prepared using the polyvinyl alcohol-protected reduction method.•The 1.95Au1Pd2/meso-Cr2O3 sample performs the best for toluene oxidation.•Oads concentration, low-temp. reducibility, and AuPd–Cr2O3 interaction govern the activity.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au, Pd, and Au–Pd (0.90 wt% Au/meso-Cr2O3, 1.00 wt% Pd/meso-Cr2O3, and xAu1Pd2/meso-Cr2O3 (x = 0.50–1.95 wt%) catalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected reduction 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 found that the meso-Cr2O3 with a high surface area of 74 m2/g was rhombohedral in crystal structure and the noble metal nanoparticles (NPs) with a size of 2.9–3.7 nm were uniformly dispersed on the surface of meso-Cr2O3. The 1.95Au1Pd2/meso-Cr2O3 sample performed the best: the T10%, T50%, and T90% (temperatures required for achieving toluene conversions of 10, 50, and 90%) were 87, 145, and 165 °C at a space velocity of 20,000 mL/(g h), respectively, and the apparent activation energy was the lowest (31 kJ/mol) among all of the samples. The effect of moisture on the catalytic activity of the 1.95Au1Pd2/meso-Cr2O3 sample was also examined. It is concluded that the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3 was associated with its small Au–Pd particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au–Pd (xAu1Pd2/meso-Cr2O3) catalysts were prepared using the KIT-6-templating and PVA-protected reduction methods, respectively. The small noble metal particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3 were responsible for the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3.

•3DOM CeO2–Al2O3 with ordered mesopore walls is fabricated via the PMMA-templating route.•3DOM 26.9CeO2–Al2O3 displays a bimodal macro/mesoporous architecture.•3DOM 26.9CeO2–Al2O3 supported noble metal is prepared via the polymer-protective reduction.•0.27Pt/3DOM 26.9CeO2–Al2O3 performs the best in toluene oxidation.•Oads content, reducibility, and noble metal—support interaction govern the catalytic activity.Three-dimensionally ordered macro-/mesoporous 26.9 wt% CeO2–Al2O3 (denoted as 3DOM 26.9CeO2–Al2O3)-supported noble metal nanocatalysts (xM/3DOM 26.9CeO2–Al2O3, x = 0.27–0.81 wt%; M = Au, Ag, Pd, and Pt) were prepared using the polymethyl methacrylate-templating and polyvinyl pyrrolidone- or polyvinyl alcohol-protected reduction methods, respectively. It is shown that the xM/3DOM 26.9CeO2–Al2O3 samples displayed a high-quality 3DOM architecture with a bimodal pore (macropore size = 180–200 nm and mesopore size = 4–6 nm) structure and a surface area of 102–108 m2/g, with the noble metal nanoparticles (3–4 nm in size) being highly dispersed on the 3DOM 26.9CeO2–Al2O3 surface. The 0.27Pt/3DOM 26.9CeO2–Al2O3 sample performed the best (T90% = 198 °C at space velocity = 20,000 mL/(g h)) for toluene oxidation. The addition of moisture to the feedstock induced a positive effect on catalytic activity. The apparent activation energies obtained over the xM/3DOM 26.9CeO2–Al2O3 samples were in the range of 46–100 kJ/mol, with the 0.27Pt/3DOM 26.9CeO2–Al2O3 sample possessing the lowest apparent activation energy. It is concluded that the good catalytic performance of 0.27Pt/3DOM 26.9CeO2–Al2O3 was associated with its higher adsorbed oxygen species concentration, better low-temperature reducibility, and stronger interaction between Pt and 3DOM 26.9CeO2–Al2O3 as well as the unique bimodal porous structure.

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and their supported gold and palladium alloy (zAuxPdy/CZY; z = 0.80–0.93 wt%; x or y = 0, 1, 2) nanoparticles (NPs) were prepared using the cetyltrimethyl ammonium bromide-assisted hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is shown that the CZY in zAuxPdy/CZY was cubic in crystal structure, surface areas of CZY and zAuxPdy/CZY were in the range 68–77 m2 g−1, and the Au–Pd NPs with a size of 4.6–5.6 nm were highly dispersed on the surface of CZY nanorods. Among all the samples, 0.90Au1Pd2/CZY possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and performed the best: T50% and T90% (temperatures required for achieving toluene conversions of 50 and 90%) were 190 and 218 °C at a space velocity of 20000 mL (g h)−1, respectively. The partial deactivation due to water vapor introduction was reversible. The active sites might be the surface oxygen vacancies on CZY, oxidized noble metal NPs, and/or interfaces between noble metal NPs and CZY. The apparent activation energies (37–43 kJ mol−1) obtained over 0.90–0.93AuxPdy/CZY were much lower than that (88 kJ mol−1) obtained over CZY for toluene oxidation. It is concluded that the excellent catalytic performance of 0.90Au1Pd2/CZY was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and CZY nanorods as well as good dispersion of Au–Pd NPs.

Using a mixture of NaNO3 and NaF as molten salt and MnSO4 and AgNO3 as metal precursors, 0.13 wt % Ag/Mn2O3 nanowires (0.13Ag/Mn2O3-ms) were fabricated after calcination at 420 °C for 2 h. Compared to the counterparts derived via the impregnation and poly(vinyl alcohol)-protected reduction routes as well as the bulk Mn2O3-supported silver catalyst, 0.13Ag/Mn2O3-ms exhibited a much higher catalytic activity for toluene oxidation. At a toluene/oxygen molar ratio of 1/400 and a space velocity of 40 000 mL/(g h), toluene could be completely oxidized into CO2 and H2O at 220 °C over the 0.13Ag/Mn2O3-ms catalyst. Furthermore, the toluene consumption rate per gram of noble metal over 0.13Ag/Mn2O3-ms was dozens of times as high as that over the supported Au or AuPd alloy catalysts reported in our previous works. It is concluded that the excellent catalytic activity of 0.13Ag/Mn2O3-ms was associated with its high dispersion of silver nanoparticles on the surface of Mn2O3 nanowires and good low-temperature reducibility. Due to high efficiency, good stability, low cost, and convenient preparation, 0.13Ag/Mn2O3-ms is a promising catalyst for the practical removal of volatile organic compounds.

In the present study, nanodisk-like Fe2O3 was first prepared using the hydrothermal method, and then its supported gold catalysts (xAu/Fe2O3 nanodisk, x = 0.71–6.55 wt %) were fabricated using the polyvinyl alcohol-protected reduction method. Under the reaction conditions of toluene concentration = 1000 ppm, toluene/O2 molar ratio = 1/400, and space velocity = 20 000 mL/(g h), 6.55Au/Fe2O3 nanodisk performed the best (T50% = 200 °C and T90% = 260 °C). The apparent activation energies (46–50 kJ/mol) obtained over the xAu/Fe2O3 nanodisk were smaller than that (65 kJ/mol) obtained over the Fe2O3 nanodisk for toluene oxidation. We conclude that the high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au nanoparticles and the Fe2O3 nanodisk are responsible for the high catalytic performance of the 6.55Au/Fe2O3 nanodisk.

High-surface-area and well-ordered mesoporous Fe-incorporated SBA-15 (xFe-SBA-15) and SBA-15-supported FeOx (yFeOx/SBA-15) with the Fe surface density between 0.09 to 1.11 Fe-atom/nm2 have been prepared using the one-step synthesis and incipient wetness impregnation methods, respectively. Physicochemical properties of these materials were characterized by means of numerous techniques, and their catalytic activities for the combustion of toluene were evaluated. It is found that the xFe-SBA-15 and yFeOx/SBA-15 samples possessed rod- or chain-like morphologies. The Fe species were of high dispersion when the Fe surface density was lower than 0.76 Fe-atom/nm2 in xFe-SBA-15 and 0.64 Fe-atom/nm2 in yFeOx/SBA-15. At a similar Fe surface density and space velocity, the xFe-SBA-15 catalysts showed better activity than the yFeOx/SBA-15 catalysts, in which the xFe-SBA-15 catalyst with Fe surface density 0.59 Fe-atom/nm2 performed the best. It is concluded that the good performance of the xFe-SBA-15 sample with Fe surface density 0.59 Fe-atom/nm2 was associated with its large surface area, high Fe species dispersion, and good low-temperature reducibility.

Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1–8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22–27 m2 g−1. The Au nanoparticles with a size of 2.4–3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of −35 °C at a space velocity of 20000 mL g−1 h−1 for CO oxidation and 256 °C at a space velocity of 40000 mL g−1 h−1 for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol−1) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol−1) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.

•CoxPd are prepared using the modified polyvinyl alcohol-protected reduction method.•CoxPd nanoparticles displayed core-shell (core: Pd; shell: Co) structure.•CoxPd nanoparticles with a core-shell structure exhibit super thermal stability.•CoxPd/3DOM CeO2 possess good O2 and CH4 adsorption abilities.•CoxPd/3DOM CeO2 perform well in methane oxidation.Three-dimensionally ordered macroporous CeO2 (3DOM CeO2) and its supported Pd@Co (CoxPd/3DOM CeO2, x (Co/Pd molar ratio) = 2.4–13.6) nanocatalysts were prepared using the polymethyl methacrylate-templating and modified polyvinyl alcohol-protected reduction methods, respectively. The Pd@Co particles displayed a core-shell (core: Pd; shell: Co) structure with an average size of 3.5–4.5 nm and were well dispersed on the surface of 3DOM CeO2. The CoxPd/3DOM CeO2 samples exhibited high catalytic performance and super stability for methane oxidation, with the Co3.5Pd/3DOM CeO2 sample showing the highest activity (T90% = 480 °C at space velocity of 40,000 mL/(g h) and excellent stability in the temperature range 400–800 °C. The apparent activation energies (58–73 kJ/mol) obtained over CoxPd/3DOM CeO2 were much lower than those (104–112 kJ/mol) over Co/3DOM CeO2 and 3DOM CeO2 for methane oxidation, with the Co3.5Pd/3DOM CeO2 sample possessing the lowest apparent activation energy (58 kJ/mol). It is concluded that the excellent catalytic performance of Co3.5Pd/3DOM CeO2 was associated with its good abilities to adsorb oxygen and methane as well as the unique core-shell structure of CoPd nanoparticles.Download high-res image (110KB)Download full-size image

•Ordered mesoporous cobalt oxide (meso-Co3O4) is obtained via KIT-6-templating route.•xAu/meso-Co3O4 nanocatalysts are prepared using the colloidal deposition method.•Au nanoparticles are highly dispersed inside the mesoporous channels of meso-Co3O4.•xAu/meso-Co3O4 perform well in the oxidation of CO, benzene, toluene, and o-xylene.•There is a strong interaction between Au nanoparticles and meso-Co3O4.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.Download high-res image (167KB)Download full-size image

•g-C3N4 is fabricated by directly heating guanidine hydrochloride.•Fe2O3/g-C3N4 is prepared by the incipient wetness impregnation method.•0.5 wt% Fe2O3/g-C3N4 possesses the highest adsorbed oxygen species concentration.•Fe2O3–g-C3N4 heterojunction inhibits the recombination of photoinduced charge carriers.•0.5 wt% Fe2O3/g-C3N4 shows excellent photocatalytic activity for 4-NP degradation.Graphitic carbon nitride and its supported iron oxide (x wt% Fe2O3/g-C3N4, x = 0.1–0.8) photocatalysts were fabricated using the guanidine hydrochloride calcination and incipient wetness impregnation methods, respectively. The x wt% Fe2O3/g-C3N4 photocatalysts contained a two-dimensional nanosheet structure with high dispersion of Fe2O3 nanoparticles (2–3 nm in size), a surface area of 27–29 m2/g, and a bandgap energy of 1.92–2.68 eV. The 0.5 wt% Fe2O3/g-C3N4 sample showed the highest photocatalytic activity (90% 4-nitrophenol (4-NP) was degraded within 40 min of visible-light illumination). Effects of pH value, H2O2 amount, and initial 4-NP concentration on activity of the typical sample were also examined. It is concluded that the enhanced photocatalytic activity of 0.5 wt% Fe2O3/g-C3N4 was associated with its unique two-dimensional layered structure, Fe2O3-g-C3N4 heterojunction, high surface oxygen adsorbed species concentration, and easy transfer and separation of photogenerated charge carriers.0.5 wt% Fe2O3/g-C3N4 exhibits excellent photocatalytic performance for 4-nitrophenol degradation, which is associated with its unique two-dimensional layered structure, Fe2O3–g-C3N4 heterojunction, and excellent separation efficiency of photoinduced electrons and holes.