•An in situ deposition route was used to prepare CuxS/TiO2 nanocomposites.•CuxS/TiO2 displayed enhanced photocatalytic H2 generation performance.•Both Cu2S and CuS facilitated the charge carriers transfer and separation.•The mechanism of enhanced photoactivity over CuxS/TiO2 was proposed.TiO2 nanoparticles functionalized with CuxS (CuxS-TiO2, x = 1 or 2) photocatalysts were synthesized via a facile precipitation method at room temperature. The resulting products were well characterized by XRD, TEM, EDS, XRF, BET, XPS, UV–vis and PL. The performance of H2 production by photocatalytic water decomposition for the CuxS-TiO2 nanocomposite was examined in methanol aqueous solution using a 300 W Xe lamp as light source. Results showed that the activities of the CuS and Cu2S dual-cocatalysts co-loaded samples exhibited highly efficient water splitting capabilities for H2 evolution, and 5.62 mmol h−1 g−1 of H2 production was achieved with the composition-optimized CuxS-TiO2, which was more efficient than those of single cocatalyst deposited samples and TiO2 alone. It is proposed that the co-deposition of CuS and Cu2S onto TiO2 nanoparticle surface could efficiently extend light absorption toward visible light range, facilitate the separation of photoinduced charge carriers and consequently enhance the photocatalytic H2 production activity. The present work not only shows the possibility for the simultaneous utilization of CuxS mixtures as efficient cocatalysts and photosensitizers to significantly facilitate the photoactivity of H2 evolution, but also offers a general, feasible strategy for constructing ternary hybrid photocatalysts with other multivalent non-noble metal compounds as cocatalysts for target applications in solar energy conversion.Download high-res image (322KB)Download full-size image

Zn-incorporated nanosized H-ZSM-5 zeolites were synthesized via a novel and facile route using zeolitic imidazolate framework-8 (ZIF-8) as the template in a steam-assisted conversion process. The prepared zeolites were characterized using various techniques including XRD, nitrogen adsorption–desorption, SEM, TEM, TGA, NH3-TPD and pyridine-FT-IR spectroscopy. The crystallization time and ZIF-8 loading were extensively investigated to elucidate the crystallization process, morphology and structural characteristics of the prepared zeolites. The results show that the formation of Zn-incorporated nanosized H-ZSM-5 zeolites involves two stages: dissolution-impregnation and crystallization. The increased amount of ZIF-8 helps to increase the number of active metal Zn sites. Furthermore, the incorporation of ZIF-8 effectively facilitates the formation of Lewis acid sites and increases the acidity. Thus, the Zn-incorporated nanosized H-ZSM-5 zeolites showed a high catalytic activity and H2 yield as well as excellent catalytic stability when used in dimethyl ether steam reforming.

•System of EY-sensitized Au/g-C3N4 NSs was constructed by a facile one-step route.•Deposition of Au and addition of EY increased visible light-harvesting capabilities.•Recombination of electron–hole pairs was effectively inhibited in water reduction.•The system displayed highly efficient photocatalytic H2 generation performance.•The mechanism of H2 evolution through solar water splitting was also discussed.In this work, uniform dispersed gold nanoparticles (Au NPs) with an average diameter of ca. 25 nm were loaded on graphitic carbon nitride nanosheets (g-C3N4 NSs) as co-catalysts via a facile one-step method. The morphology, composition, and crystallinity of the as-prepared products were well characterized by a variety of analytical methods. Results showed that the Au/g-C3N4 nanocomposite plasmonic photocatalysts with optimal loading of 2.0 wt% Au exhibited the highest photoactivity for H2 production under visible light irradiation (λ ≥ 400 nm) using triethanolamine (TEOA) as sacrificial reagents, which was almost 5.3 times higher than pure g-C3N4. In addition, through directly adding a cheap dye Eosin Y (EY) into the reaction suspension, the photocatalysis system showed a dramatically enhanced H2 evolution rate of 660.8 μmol/h•g that was about 3.5 times higher than that of the 2.0 wt% Au/g-C3N4 composite. It is proposed that the combination of dye sensitization with EY and plasmonic modification with Au NPs for g-C3N4 NSs could efficiently increase the density of photogenerated electron–hole pairs, facilitate the separation of charge carriers and consequently enhance the photoactivity for H2 evolution. The present work not only shows the possibility for the utilization of EY as an efficient photosensitizer and Au as H2 production co-catalysts to co-promote the photocatalytic performance of g-C3N4, but also offers a simple, low-cost, and convenient method for constructing other efficient plasmonic-metal/semiconductor heterostructures for plasmon-enhanced photocatalytic applications.Visible-light-active Au/g-C3N4 nanocomposites sensitized by EY showed efficient photo-induced charge-transfer property and enhanced photocatalytic H2 generation activity from water splitting.Download high-res image (111KB)Download full-size image

•Highly efficient MOF-templated Ni catalyst was applied to hydrogen purification.•The catalyst has small crystallite size and high dispersion of Ni nanoparticles.•The catalyst has a wide working temperature window (215–350 °C) for CO-SMET.•The catalyst had high stability during a long-term durability test (120 h).Highly efficient and non-noble metal-based Ni/ZrO2 catalyst templated with Ni/UiO-66 precursor was successfully prepared and applied to CO selective methanation in H2-rich gases. This catalyst showed excellent activity and selectivity in an extremely wide temperature window of 215–350 °C, and it also had high stability with no deactivation during a long-term stability test (120 h). The increased specific surface area, smaller crystallite size (3.5 nm) and higher dispersion (15.3%) of Ni nanoparticles, and the enhanced chemisorption capability for CO might contribute to its excellent performance.Download high-res image (192KB)Download full-size image

•One step evaporation-induced self-assembly method was proposed to in situ fabricate Ni-Al-oxide/Ni-foam monolithic support.•Ni-Al-oxide/Ni-foam composite as support couples merits of more active sites with superior thermal conductivity.•Ru/Ni-Al-oxide/Ni-foam composite catalyst exhibits an excellent performance for CO selective methanation.An evaporation-induced self-assembly method was employed for the first time to prepare Ni-Al-oxide/Ni-foam composites as support for a novel Ru/Ni-Al-oxide/Ni-foam 3D composite catalyst, which was utilized to effectively deep-remove CO in hydrogen-rich gas for fuel cell applications. The characterizations of BET, XRD, SEM and TEM show that a mesoporous Ni-Al oxide was constructed on Ni foam via this feasible way with specific surface area as high as 42 m2 g− 1, which assured a uniform dispersion of Ru nano-particles. The resultant monolithic catalysts exhibit an excellent performance for CO selective methanation, which may be attributed to its unique high specific surface area for more active sites and high thermal conductivity for avoiding the formation of local hot spots. The CO outlet concentration in hydrogen-rich gas can be decreased down to as low as less than 10 ppm from a high level of 1 vol% in a wide working temperature range of 180–280 °C, while the CH4 outlet concentration is less than 2 vol%.

•A facile and cost effective method of precipitation to synthesis P-CdS composite photocatalysts.•The catalyst has improved charge-separation efficiency and increased charge carrier lifetime.•Photocatalytic H2 evolution activity of red P modified CdS is significantly enhanced.•The composite catalyst remained perfective stability and activity even after five cycles.Novel red phosphorus-CdS (P-CdS) composite photocatalysts were successfully prepared through a facile and fast precipitation method. The samples were then characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) and photoluminescence emission spectroscopy (PL). The photocatalytic activity was evaluated by H2 generation in the aqueous solution containing Na2S/Na2SO3 as hole scavengers under visible light irradiation (λ ≥ 400 nm). The results show the optimal P molar ratio was 10 mol% and the corresponding H2 production rate reached 923 umol h−1 g−1, which is about 2.53 times higher than that of CdS sample. Meanwhile, the composite photocatalysts show favorable photostability. The enhanced photocatalytic activity can be attributed to the highly effective charge separation on P-CdS hybrids as confirmed by PL result. Also, a possible photocatalytic mechanism of the P-CdS composites is proposed and discussed in detail.

•A facile precipitation route was used to prepare Co(OH)2/TiO2 nanocomposites.•The Co(OH)2/TiO2 photocatalyst has improved charge-separation efficiency.•The H2 evolution performance of Co(OH)2 modified TiO2 is significantly enhanced.Co(OH)2 modified TiO2 (Co(OH)2/TiO2) photocatalysts were fabricated by a simple precipitation method and characterized by XRD, TEM, N2-physisorption, UV–vis DRS and PL. The photocatalytic H2 evolution performance on TiO2 was significantly enhanced by loading Co(OH)2. The optimum Co(OH)2 loading content was found to be 0.25 mol%, yielding a H2-evolution rate of 1946 μmol h−1 g−1, being about 23 times of that on pure TiO2. This enhancement of photocatalytic H2 evolution was attributed to the Co(OH)2 clusters deposited on TiO2 surface, which can act as electron traps and thus facilitate the charge carrier separation.

Noble-metal-free Cu(OH)2/TNTs (TNTs: TiO2 nanotubes) nanocomposite photocatalysts were successfully prepared by loading nano-Cu(OH)2 on TNTs via a hydrothermal-precipitation process. These were then characterized in terms of morphology and physicochemical properties by employing TEM, XRD, XPS, BET, UV–Vis DRS and PL. The effects of Cu(OH)2 loading, amount of catalyst on the photocatalytic hydrogen production performance of Cu(OH)2/TNTs were investigated in detail in aqueous methanol solution under UV irradiation. The results show that, compared with pure TNTs, the TNTs loaded with highly dispersed 8 wt% Cu(OH)2 exhibited remarkably improved activity for hydrogen production (the largest quantity of evolved hydrogen was ca. 14.94 mmol h−1 g−1 catalyst) with good photostability. This high activity is attributed to the strong synergistic function of Cu(OH)2/TNTs, including suitable potential of Cu(OH)2/Cu (E0 = −0.222 V) between conduction band (−0.260 V) of TNTs and the reduction potential of H+/H2 (E0 = 0.000 V), a unique tubular microstructure of TNTs coated with nano-Cu(OH)2, large BET specific surface area and high dispersion of Cu(OH)2. Furthermore, a process mechanism for methanol/water decomposition over Cu(OH)2/TNTs is proposed to understand its high activity.Highlights► Cu(OH)2/TNTs photocatalysts were prepared by a hydrothermal-precipitation process. ► Coupling of TNTs with nano-Cu(OH)2 greatly enhanced photocatalytic hydrogen production. ► This improved activity is due to the strong synergistic function of Cu(OH)2/TNTs. ► A possible mechanism for methanol/water decomposition over Cu(OH)2/TNTs is proposed.

•A facile and green hydrothermal method was used to prepare TNT/GR.•The reduction of GO and formation of 1-D TNT were achieved simultaneously.•The TNT/GR photocatalyst has improved charge-separation efficiency.•The H2 evolution activity of TNT/GR is significantly enhanced.A facile and green one-step method was used to prepare titanate nanotube/graphene (TNT/GR) photocatalysts via an alkaline hydrothermal process. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence emission spectroscopy. The photocatalytic performance was evaluated by H2 generation from water splitting under Xe-lamp illumination. A significantly enhanced photocatalytic activity for H2 evolution (12.1 μmol/h) was obtained over the compostion-optimized TNT/GR composite (with 1.0 wt% GR), two times higher than that of pure TNT (4.0 μmol/h). During hydrothermal reaction, the reduction of graphene oxide (GO) into GR without using any reducing agents and the formation of 1-D TNT were achieved simultaneously, which resulted in the direct growth of well-defined TNTs uniformly distributed on GR substrates.

Uniformly dispersed Ni catalysts supported on SiO2 wash-coated Ni foams were synthesized by the wet impregnation method and successfully applied for methane catalytic decomposition (MCD) at atmospheric pressure. All the prepared catalysts exhibited high catalytic stability. The effects of reaction temperature, space velocity, Ni loading on the MCD performance and the morphologies of the as-prepared CNTs were investigated. The results show that high reaction temperature, low space velocity, and high Ni loading enhanced the hydrogen concentration in the outlet gases. Additionally, SEM and TEM observations indicate that the size (diameter) distribution of the as-prepared CNTs became broader with increasing reaction temperature and Ni loading, respectively. The uniform nickel-foam-supported CNTs and relatively high concentration of hydrogen were obtained simultaneously at 650 °C and at a weight hourly space velocity of 1 L g−1cat h−1 by the catalyst with 20 wt% Ni. Raman spectroscopy reveals that the uniform MCNTs had a high degree of amorphization.Highlights► Ni metal foam was employed to produce Ni foam supported CNTs. ► The uniformly dispersed Ni catalysts supported on Ni foam were synthesized. ► The Ni foam supported CNTs and hydrogen were obtained simultaneously.

Amorphous Ni–Ru–B/ZrO2 catalyst was prepared by the means of chemical reduction, and selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over the amorphous Ni–Ru–B/ZrO2 catalyst. The result showed that, at the temperature of 210–230 °C, the catalyst was shown to be capable of reducing CO in a hydrogen-rich reformate to less than 10 ppm, while keeping the CO2 conversion below 1.55% and the hydrogen consumption below 6.50%.

The activities of CuO–CeO2–ZrO2 catalysts synthesized by four methods, e.g. sol–gel, co-precipitation, one-step impregnation, and two-step impregnation, were compared for CO removal from hydrogen-rich gas. The influence of the precipitant and calcination temperature on the catalytic activity was investigated, and a series of analytical methods, such as XRD, H2-TPR, TG-DSC, and SEM, were used to characterize the catalysts. It was indicated that CuO–CeO2–ZrO2 catalyst prepared by co-precipitation method exhibits the widest operation temperature range with the 99% conversion of CO and relatively high selectivity. The optimized preparation conditions were confirmed using Na2CO3 as a precipitant, and calcining at 500 °C. It was proposed that the high activity and selectivity result from the high dispersion of copper and strong interaction among CuO, CeO2, and ZrO2. The effects of precipitants on the grain size and morphology of the catalyst is larger than that of calcination temperature.

Amorphous Ni-Ru-B/ZrO2 catalysts were prepared by chemical reduction method. The effects of Ni-Ru-B loading and Ru/Ni mole ratio on the catalytic performance for selective CO methanation from reformed fuel were studied, and the catalysts were characterized by BET, ICP, XRD and TPD. The results showed that Ru strongly affected the catalytic activity and selectivity by increasing the thermal stability of amorphous structure, promoting the dispersion of the catalyst particle, and intensifying the CO adsorption. For the catalysts with Ru/Ni mole ratio under 0.15, the CO methanation conversion and selectivity increased significantly with the increasing Ru/Ni mole ratio. Among all the catalysts investigated, the 30 wt% Ni-Ru-B loading amorphous Ni61Ru9B30/ZrO2 catalyst with 0.15 Ru/Ni mole ratio presented the best catalytic performance, over which higher than 99.9% of CO conversion was obtained in the temperature range of 230°C∼250°C, and the CO2 conversion was kept under the level of 0.9%.

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h−1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction (XRD) and temperature programmed reduction (TPR) measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7 Oδ catalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2 Zr0.1 Al0.7 Oδ autothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ was found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1−xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1−xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.

The Ni-B-Oδ and Ni-B-Zr-Oδ catalysts were prepared by the method of chemical reduction, and the deep removal of CO by selective methanation from the reformed fuels was performed over the as-prepared catalysts. The results showed that zirconium strongly influenced the activity and selectivity of the Ni-B-Zr-Oδ catalysts. Over the Ni-B-Oδ catalyst, the highest CO conversion obtained was only 24.32% under the experimental conditions studied. However, over the Ni-B-Zr-Oδ catalysts, the CO methanation conversion was higher than 90% when the temperature was increased to 220 °C. Additionally, it was found that the Ni/B mole ratio also affected the performance of the Ni-B-Zr-Oδ catalysts. With the increase of the Ni/B mole ratio from 1.8 to 2.2, the CO methanation activity of the catalyst was improved. But when the Ni/B mole ratio was higher than 2.2, the performance of the catalyst for CO selective methanation decreased instead. Among all the catalysts, the Ni29B13Zr58Oδ catalyst investigated here exhibited the highest catalytic performance for the CO selective methanation, which was capable of reducing the CO outlet concentration to less than 40 ppm from the feed gases stream in the temperature range of 230–250 °C, while the CO2 conversion was kept below 8% all along. Characterization of the Ni-B-Oδ and Ni-B-Zr-Oδ catalysts was provided by XRD, SEM, DSC, and XPS.

Dense membrane with the composition of SrFe0.6Cu0.3Ti0.1O3−δ (SFCTO) was prepared by solid state reaction method. Oxygen permeation flux through this membrane was investigated at operating temperature ranging from 750°C to 950°C and different oxygen partial pressure. XRD measurements indicated that the compound was able to form single-phased perovskite structure in which part of Fe was replaced by Cu and Ti. The oxygen desorption and the reducibility of SFCTO powder were characterized by thermogravimetric analysis and temperature programmed reduction analysis, respectively. It was found that SFCTO had good structure stability under low oxygen pressure at high temperature. The addition of Ti increased the reduction temperature of Cu and Fe. Performance tests showed that the oxygen permeation flux through a 1.5 mm thick SFCTO membrane was 0.35–0.96 ml·min−1·cm−2 under air/helium oxygen partial pressure gradient with activation energy of 53.2 kJ·mol−1. The methane conversion of 85%, CO selectivity of 90% and comparatively higher oxygen permeation flux of 5 ml·min−1·cm−2 were achieved at 850°C, when a SFCTO membrane reactor loaded with Ni-Ce/Al2O3 catalyst was applied for the partial oxidation of methane to syngas.

Series of carbon nanotube supported Ru-based catalysts were prepared by impregnation method and applied successfully for complete removal of CO by CO selective methanation from H2-rich gas stream conducted in a fixed-bed quartz tubular reactor at ambient pressure. It was found that the metal promoter, reduction temperature and metal loading affected the catalytic properties significantly. The most excellent performance was presented by 30 wt% Ru-Zr/CNTs catalyst reduced at 350 °C. Since it decreased CO concentration to below 10 ppm from 12000 ppm by CO selective methanation at the temperature range of 180–240 °C, and kept CO selectivity higher than 85% at the temperature below 200 °C. Characterization using XRD, TEM, H2-TPR and XPS suggests that Zr modification of Ru/CNTs results in the weakening of the interaction between Ru and CNTs, a higher Ru dispersion and the oxidization of surface Ru. Amorphous and high dispersed Ru particles with small size were obtained for 30 wt% Ru-Zr/CNTs catalyst reduced at 350 °C, leading to excellent catalytic performance in CO selective methanation.

TiO2 nanotubes (TNTs) with nickel sulfide (NiS) co-catalyst were prepared by a simple solvothermal method and characterized by X-ray diffraction, transmission electron microscope, N2-physisorption, UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. Loading NiS nano-clusters can significantly enhance the photocatalytic H2 evolution performance of TNTs. The optimum NiS loading content was found to be 8 wt% and the corresponding hydrogen production rate is ca. 7486 µmol/h/g, being about 79 times higher than that of pure TNTs. This enhancement of photocatalytic H2 evolution was attributed to the synergistic effect between NiS and TNTs.Download high-res image (88KB)Download full-size imageNiS is firstly used as co-catalyst to modified TNTs, and the synergistic effect between NiS and TNTs can promote photo electrons transferring quickly from TNTs to NiS, which can promote photocatalyst’s H2 production activity.

The Ru/Al2O3 catalysts modified with metal oxide (K2OandLa2O3) were prepared via incipient wetness impregnation method from RuCl3·nH2O mixed with nitrate loading on Al2O3 support. The activity of catalysts was evaluated under simulative conditions for the preferential oxidation of CO (CO-PROX) from the hydrogen-rich gas streams produced by reforming gas, and the performances of catalysts were investigated by XRD and TPR. The results showed that the activity temperature of the modified catalysts Ru-K2O/Al2O3 and Ru-La2O3/Al2O3 were lowered approximately 30 °C compared with pure Ru/Al2O3, and the activity temperature range was widened. The conversion of CO on Ru-K2O/Al2O3 and Ru-La2O3/Al2O3 was above 99% at 140–160 °C, suitable to remove CO in a hydrogen-rich gas and the selectivity of Ru-La2O3/Al2O3 was higher than that of Ru-K2O/Al2O3 in the active temperature range. Slight methanation reaction was detected at 220 °C and above.