Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

Cu was loaded on the S-doped TiO₂ by electroless plating method. The prepared Cu/S–TiO₂ exhibited high photocatalytic activity for hydrogen generation, and the yield is up to 7.5 mmol h^− 1 g^− 1cat in methanol solution. Their physical structure and chemical properties were characterized by UV–Vis, XRD, XPS and EXAFS. The copper species were CuO and Cu₂O, and the sample showed excellent visible light absorption ability. Comparing with the sample prepared by chemical reducing method, the electroless plated copper on S–TiO₂ was highly dispersed, which could facilitate photo-generated charges capture, transfer and separation.     

Photocatalytic Cancer (HeLa) Cell-Killing Enhanced with Cu–TiO2 Nanocomposite

The metallic Cu nanoparticles have been successfully deposited on the heterogeneous TiO₂ surface by the borohydride reduction of copper nitrate in water/CH₃CN mixture under Ar atmosphere. The catalytic activity of the Cu–TiO₂ nanocomposite was evaluated by the application to a photocatalytic cancer cell-killing under UV–visible light irradiation. Based on the obtained results, a plausible mechanism was proposed.     

Catalytic combustion of methane over M (Ni,Co, Cu) supported on ceria–magnesia

The catalytic activity of a series of M(= Ni, Co, Cu)/(CeO₂)_x–(MgO)_1 − x catalysts for methane combustion was investigated. (CeO₂)_x–(MgO)_1 − x supports were prepared by a sol-gel method. The influence of CeO₂ content and active components such as Ni, Co and Cu are discussed. The results indicate that the activity of the catalysts depends strongly on CeO₂ content. The Ni/(CeO₂)_0.1 − (MgO)_0.9 catalyst showed the highest catalytic activity and good thermal stability for methane combustion. The highly dispersed NiO is the main active site for methane combustion. Fresh M (Ni, Co and Cu)/(CeO₂)_0.1–(MgO)_0.9 catalysts showed that the activity of CuO for methane combustion was slightly higher than that of NiO and CoO, while the thermal stability increased in the order Cu < Co < Ni. Cu/(CeO₂)_0.1–(MgO)_0.9 catalyst was sintered after a second evaluation. Consequently, (CeO₂)_0.1–(MgO)_0.9 is deemed to be a good support for Ni.     

Hydrogen production via methanol steam reforming over Au/CuO,Au/CeO2, and Au/CuO–CeO2 catalysts prepared by deposition–precipitation

The production of hydrogen (H₂) with a low concentration of carbon monoxide (CO) via steam reforming of methanol (SRM) over Au/CuO, Au/CeO₂, (50:50)CuO–CeO₂, Au/(50:50)CuO–CeO₂, and commercial MegaMax 700 catalysts were investigated over reaction temperatures between 200 °C and 300 °C at atmospheric pressure. Au loading in the catalysts was maintained at 5 wt%. Supports were prepared by co-precipitation (CP) whilst all prepared catalysts were synthesized by deposition–precipitation (DP). The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM). Au/(50:50)CuO–CeO₂ catalysts expressed a higher methanol conversion with negligible amount of CO than the others due to the integration of CuO particles into the CeO₂ lattice, as evidenced by XRD, and a interaction of Au and CuO species, as evidenced by TPR. A 50:50 Cu:Ce atomic ratio was optimal for Au supported on CuO–CeO₂ catalysts which can then promote SRM. Increasing the reaction time, by reducing the liquid feed rate from 3 to 1.5 cm³ h^?1, resulted in a catalytic activity with complete (100%) methanol conversion, and a H₂ and CO selectivity of ～82% and ～1.3%, respectively. From stability testing, Au/(50:50)CuO–CeO₂ catalysts were still active for 540 min use even though the CuO was reduced to metallic Cu, as evidenced by XRD. Therefore, it can be concluded that metallic Cu is one of active components of the catalysts for SRM.     

The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.     

Selective oxidation of CO in hydrogen atmosphere on Pt–Fe catalysts supported on zeolite P-based materials

The catalytic properties of Pt supported on zeolite P (ZP)-based materials for the preferential CO oxidation in hydrogen atmosphere under mild conditions (from room temperature to 150 °C), have been investigated. Pt catalysts (1–4 wt%) supported on a zeolitized pumice support (Z-PM) have been prepared. A series of bimetallic Pt–Fe on ZP, having 2 wt% Pt and different Fe loading (0.5–4 wt%), have been also prepared and used as model catalysts. A detailed characterization of the catalysts has been carried out by means of surface area and porosity measurements, X-ray diffraction, scanning electron microscopy and transmission electron microscopy in order to investigate the morphological and microstructural properties of both support and catalytic system. Pt/Z-PM exhibited complete CO conversion with 55 % selectivity at temperatures as low as 50 °C, with no noticeable degradation of the catalytic performances, indicating that the Fe content present as an impurity in the zeolitized pumice support allows to obtain catalysts characterized by high activity and stability. On the basis of the characterization and kinetic tests, hypotheses on the role of Fe promoter have been formulated.     

Ruthenium supported on new TiO2–ZrO2 systems as catalysts for the partial oxidation of methane

The partial oxidation of methane is studied at 673–873 K over new Ru-based catalysts supported on TiO₂–ZrO₂ with different TiO₂ content. Supports were prepared by a sol–gel method, and RuCl₃ and RuNO(NO₃)₃ were used as ruthenium precursors to prepare the catalysts (1–2 wt% Ru). The effect of the reaction temperature on the catalytic behavior is analyzed, along with the support composition and the Ru precursor used.     

Selective catalytic Knoevenagel condensation by Ni–SiO2 supported heterogeneous catalysts: An environmentally benign approach

Selective catalytic Knoevenagel condensation is achieved with catalytic amounts of Ni impregnated on SiO₂ or TiO₂ supports. In this liquid phase reaction, quantitative yields were obtained under mild reaction conditions. Ni–SiO₂, Ni–TiO₂ catalysts showed efficiency of 100% conversion and 100% selectivity. With smaller quantities of 10% Ni–SiO₂ took less duration for the completion of reaction than TiO₂ catalysts in this environmentally benign process.     

Ni(II)–Mg(II)–Al(III) catalysts for hydrogen production from ethanol steam reforming: Influence of the activation treatments

The effect of the Ni(II)–Mg(II)–Al(III) layered double hydroxide (LDH) activation conditions over the surface and bulk composition and the catalytic performance in ethanol steam reforming (ESR) is studied. Ternary oxides were prepared by thermal decomposition of LDHs synthesized using the homogeneous precipitation method with urea. Catalyst precursor is submitted to two different activation treatments: calcinations at 400, 500, 600 and 700 °C with subsequent reduction at 720 °C, or direct reduction at 720 °C. The samples were characterized by sorptometry, H₂ chemisorption, ICP chemical analysis, thermogravimetric analysis, X-ray diffraction, X-ray photoelectronic spectroscopy and temperature programming reduction. The catalysts obtained by calcination at 600 °C and then reduction at 720 °C and those directly reduced at 720 °C showed the better performance in ESR. The precursor submitted to a proper thermal treatment develops, through a decoration-demixing process, a Ni(II)-poor spinel-type shell onto NiO domains.     

Synthesis of a Ni2P catalyst supported on anatase–TiO2 whiskers with high hydrodesulfurization activity,based on triphenylphosphine

A solution method for preparing a Ni₂P catalyst supported on anatase–TiO₂ whiskers (Ni₂P–PPh₃) based on low cost triphenylphosphine (PPh₃) is described. This approach suppressed the formation of the TiPO₄ phase. The synthesis temperature is modest (603 K). The Ni₂P–PPh₃ catalyst did not modify the anatase–TiO₂ phase in any way, and it showed much higher hydrodesulfurization activity than the same catalyst prepared by the conventional TPR method.     

HI decomposition over active carbon supported binary Ni–Pd catalysts prepared by electroless plating

A series of binary Ni–Pd catalysts supported on active carbon was prepared by electroless plating method. For comparison, active carbon supported monometallic Pd and Ni catalysts were also prepared by liquid-phase reduction. Among the Pd, Ni and binary Ni–Pd catalysts, the catalyst of 1%Ni–1%Pd/C showed the best catalytic performance for the decomposition of HI. Furthermore, characterizations by BET and XRD revealed that the binary Ni–Pd catalyst had the higher stability in specific surface area and structure than monometallic Pd catalyst during HI decomposition.     

Characterization and catalytic properties of Ni and NiCu catalysts supported on ZrO2–SiO2 for guaiacol hydrodeoxygenation

ZrO₂–SiO₂ complex oxides with Si/Zr mole ratio of 3 (SZ-3) were synthesized. ZrO₂–SiO₂ supported Ni and NiCu catalysts were prepared by impregnation method. Their catalytic performances were evaluated in the hydrodeoxygenation (HDO) upgrading of model reactant guaiacol to hydrocarbons. The physicochemical properties of the support materials and catalysts were characterized by FTIR, XRD, TPD, TPR, and BET techniques. The addition of Cu significantly affected the acidity, and thus influenced their catalytic performance for product distributions. Over the Ni5Cu/SZ-3 catalyst, the cyclohexane selectivity of 80.8% and the methylcyclohexane selectivity of 12.4% were obtained with complete conversion of guaiacol under the 300 °C, 5.0 MPa H₂ pressure.     

Renewable hydrogen production from steam reforming of glycerol (SRG) over ceria-modified γ-alumina supported Ni catalyst

Excess crude glycerol derived as a by-product from biodiesel industry prompts the need to valorise glycerol to value-added chemicals. In this context, catalytic steam reforming of glycerol (SRG) was proposed as a promising and sustainable alternative for producing renewable hydrogen (H₂). Herein, the development of nickel (Ni) supported on ceria-modified mesoporous γ-alumina (γ-Al₂O₃) catalysts and their applications in catalytic SRG (at 550–750 °C, atmospheric pressure and weight hourly space velocity, WHSV, of 44,122 ml·g⁻¹·h⁻¹ (STP)) is presented. Properties of the developed catalysts were characterised using many techniques. The findings show that ceria modification improved Ni dispersion on γ-Al₂O₃ catalyst support with highly active small Ni particles, which led to a remarkable catalytic performance with the total glycerol conversion (ca. 99%), glycerol conversion into gaseous products (ca. 77%) and H₂ yield (ca. 62%). The formation rate for H₂ production (14.4 × 10⁻⁵ mol·s⁻¹·g⁻¹, TOF (H₂) = 3412 s⁻¹) was significantly improved with the Ni@12Ce-Al₂O₃ catalyst, representing nearly a 2-fold increase compared with that of the conventional Ni@Al₂O₃ catalyst. In addition, the developed catalyst also exhibited comparatively high stability (for 12 h) and coke resistance ability.     

Hydrogen production by ethanol reforming over Rh/CeO2–ZrO2 catalysts

Reforming of ethanol in excess of water (1–8 molar ratio) has been investigated on Rh/CeO₂, Rh/ZrO₂ and Rh/CeO₂–ZrO₂ (Ce/Zr=4, 2 and 1). Catalysts characterization was conducted by X-ray diffraction, BET surface area measurements, CO₂ adsorption, and temperature programmed reduction (TPR). At 400–500 °C all catalysts showed high activity and selectivity towards hydrogen production (between 5 and 5.7 mol of H₂ per mol of ethanol inlet) despite the considerable textural differences of the oxides (fluorite, monoclinic and tetragonal). The large variations of Rh dispersion (as monitored by TPR) between all catalysts had a small effect on H₂ production. Although it appears that the reaction is not sensitive to either the oxide or the metal structure Rh/CeO₂ (the most basic catalyst investigated) was the least reactive.     

Structure–Activity Correlations for Au Nanoclusters Supported on TiO2

The catalytic performance of reducible metal-oxide-supported Au nanoclusters displays striking dependencies on several factors such as dispersion, support, pretreatment, and preparation methods. Planar model Au/TiO₂ catalysts have been prepared in ultrahigh vacuum in order to investigate the strong size dependence of low-temperature CO oxidation. It is demonstrated that the experimentally observed structure sensitivity of CO oxidation on Au/TiO₂ may be rationalized by a quantum size effect. Via scanning tunneling microscopy and spectroscopy (STM/STS) and elevated pressure reaction kinetics measurements, we show that a clear correlation exists between the structural, electronic, and reactivity properties of supported Au nanoclusters.     

Water-gas shift reaction over Cu–Zn,Cu–Fe,and Cu–Zn–Fe composite-oxide catalysts prepared by urea-nitrate combustion

Water-gas shift reaction was investigated over Cu–Zn, Cu–Fe and Cu–Zn–Fe composite-oxide catalysts at atmospheric pressure from 200 to 375 °C in terms of reducing the CO content with maximal H₂ yield. The Cu_0.15ZnFe₂ spinel catalyst expressed a higher CO conversion level and H₂ yield at a lower temperature compared to the Cu_0.15Zn and Cu_0.15Fe catalysts. Adding H₂O to the feed up to 30% (v/v), but not above, increased the CO reduction level, presumably by increasing the hydroxyl species to react with the adsorbed CO. Increasing the W/F ratio to 0.24 g s cm^?3 increased the CO conversion level to 0.76 at 275 °C with the Cu_0.15ZnFe₂ catalyst, and could be further increased to 0.86 at 350 °C by increasing the Cu molar ratio to 0.30 (Cu_0.30ZnFe₂). Nevertheless, increasing the Cu molar content to 0.50 reduced the CO conversion level. No requirement for adding O₂ when using the Cu_0.30ZnFe₂ catalyst at >260 °C was observed. Increasing the CO content in the reactant decreased its conversion level. The performance of the Cu_0.30ZnFe₂ catalyst was stable over a test period in a CO-rich condition. No undesired product was detected, suggesting a higher selectivity for hydrogen production with a low CO content.     

Effect of calcination temperature of mesoporous nickel–alumina catalysts on their catalytic performance in hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous nickel–alumina (Ni–A-NS) catalysts prepared by a non-ionic surfactant-templating method were calcined at various temperatures for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of nickel–alumina catalysts on their physicochemical properties and catalytic activity for steam reforming of LNG was investigated. Nickel oxide species were finely dispersed on the surface of Ni–A-NS catalysts through the formation of nickel aluminate phase. Reducibility, nickel surface area, and nickel dispersion of Ni–A-NS catalysts decreased with increasing calcination temperature. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas decreased with increasing calcination temperature of Ni–A-NS catalysts. Nickel surface area and reducibility of Ni–A-NS catalysts were well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni–A-NS700 (nickel–alumina catalyst calcined at 700 °C) with the highest nickel surface area and the highest reducibility exhibited the best catalytic performance.     

Hydrogenation of Carbon Dioxide on Rh, Au and Au–Rh Bimetallic Clusters Supported on Titanate Nanotubes, Nanowires and TiO2

Supported gold, rhodium and bimetallic rhodium-core?Cgold-shell catalysts were prepared. The supports were TiO₂ as well as titanate nanotube and nanowire formed in the hydrothermal conversion of titania. The catalytic properties were tested in the CO₂ hydrogenation at 493?K. The amount and the reactivity of the surface carbonaceous deposit were determined by temperature-programmed reduction. The surfaces of the materials were characterized by X-ray photoelectron and low-energy ion scattering spectroscopy (LEIS). The surface forms during the catalytic reaction were identified by DRIFT spectroscopy. On the XP spectra of bimetallic catalysts the existence of highly dispersed gold particles could be observed besides the metallic form on all supports. Small Rh particles could also be identified on the titanate supports. LEIS spectra demonstrated that Rh-core?CAu-shell particles formed, since no scattering from Rh was detected. The main product of CO₂ hydrogenation was CH₄ on all catalysts. IR spectra revealed the existence of CO and formate species on the surface. In addition, a new band was observed around 1,770?cm^?1 which was assigned as tilted CO. It is bonded to Rh and interacts with a nearby the oxygen vacancy of the support. Agglomeration of highly dispersed Rh was observed on bimetallic samples induced by reaction or reactant.     

Combustion synthesis and electrophysical properties of hollandites of the system K2O–MeO–TiO2 (Me = Mg,Ni, Cu)

Hollandite-based ceramics are mainly produced by the traditional solid-phase method. However, the use of “wet” chemistry can improve its morphological characteristics, increase porosity, etc., as well as change the electrophysical properties. In this study complex oxides with hollandite-type structure in the system K₂O–MeO–TiO₂ (Me = Mg, Ni, Cu) were synthesized by combustion of citrate–nitrate compositions (a special case of the sol–gel method). The structure of obtained material was studied using the XRD and SEM analysis. While studying the electrophysical properties, it was found that in a stream of hydrogen, the electrical conductivity of hollandites with magnesium and nickel increases significantly (by 2–3 orders of magnitude) over the entire studied temperature range. Thus, ceramics based on these hollandites can be used to create hydrogen sensors.