Role of Pt in the Activity and Stability of PtNi/CeO2–Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO₂/Al₂O₃. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H₂-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO₂–Al₂O₃ catalyst in ethanol steam reforming, in terms of lower formation of coke, C₂ secondary products and a constant production of CO₂ and H₂. The amount and type of carbon deposited on the catalyst was analyzed by TG–TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved. This Pt–Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt⁰, Ni⁰ and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C–C bond breakage, Pt particles enhance the hydrogenation of coke precursors (C_xH_y) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.     

Role of Pt Oxidation State on the Activity and Selectivity for Crotonaldehyde Hydrogenation Over Pt–Sn/Al2O3–La and Pt–Pb/Al2O3–La Catalysts

Pt–Sn/ALa10 and Pt–Pb/ALa10 catalysts (10 wt% La₂O₃) were studied in the selective hydrogenation of crotonaldehyde. Oxidized Pt²⁺ and reduced Pt⁰ species were identified by XPS on the bimetallic catalysts. High selectivity to crotylalcohol was obtained on the Pt–Pb/ALa10 catalyst where an electron transfer effect from Pb to Pt was proposed. For the Pt–Sn/ALa10 catalyst the formation of Pt–SnO _x –La₂O₃ complexes showing low activity and low selectivity was inferred.     

Oxidative Steam Reforming of Ethanol over Ni–Cu/SiO2, Rh/Al2O3 and Ir/CeO2: Effect of Metal and Support on Reaction Mechanism

The effect of metal and support on ethanol oxidative steam reforming (OSR) has been investigated over a series of stable and active catalytic systems with noble (Rh or Ir) and non noble metal (Ni–Cu) supported over neutral (SiO₂), amphoteric (Al₂O₃) or redox (CeO₂) supports. Ethanol decomposition and oxidative steam reforming was investigated by in situ diffuse reflectance infrared spectroscopy under temperature-programmed desorption and surface reaction conditions. Different mechanisms were established for these systems, from the initial steps of ethanol activation to the final equilibration of the decomposition products CO, CO₂, H₂ and H₂O. Various intermediates such as formates, acetates and/or carbonates were found to play different roles depending on the catalyst composition. The stability and activity of the investigated systems were finally assigned to specific features of these mechanisms.     

Effect of Acid–Base Properties on the Catalytic Activity of Pt/Al2O3 Based Catalysts for Diesel NO Oxidation

The activity of Pt catalysts supported on Al₂O₃ modified with various acid–base additives has been investigated for oxidation of NO to NO₂. Although Pt dispersion was changed by the additives, there was no clear effect of Pt dispersion on the catalytic activity. The measurement of solid acid–base properties of the modified Pt/Al₂O₃ indicated that the NO oxidation activity increased by the increase of surface density of strong acid sites and decreased by the increase of basic sites. It was suggested that platinum on the acidic supports keeps its highly active metallic state for NO oxidation, while the formation of nitrate/nitrite on the basic supports inhibits the reaction on the Pt surface.     

Insights into SO2 Interaction with Pd/Co3O4–CeO2 Catalysts for Methane Oxidation

The catalytic performance and the sulphur resistance of a Pd (0.7 wt%) catalyst supported over Co₃O₄(30 wt%)–CeO₂(70 wt%) mixed oxide were investigated in the oxidation of methane under stoichiometric and lean conditions. The catalytic behaviour was compared with that of two reference catalysts, palladium supported over pure Co₃O₄ and CeO₂. Catalysts were characterized by XRD, BET, XPS and FTIR measurements. Regeneration by a CH₄-reducing treatment at 600 °C was investigated.     

Autothermal Reforming of Methane Over CeO2–ZrO2–La2O3 Supported Rh Catalyst

Autothermal reforming of methane was studied over La-doped ceria–zirconia-supported Rh catalysts. The CH₄ conversion increased from 49 to 60% on increasing the content of La³⁺ from 5 to 15%, while further increase in the La³⁺ content led to a slight decrease on both CH₄ conversion and H₂ selectivity. H₂-TPR and UV–vis DRS spectrum showed that the interaction between Rh and the support was enhanced by increasing the content of La. We speculated that a so-called “Rh–La interfacial species” was formed on the surface of the support, which played an important role in catalytic activity. The balance between exposed Rh and the “Rh–La interfacial species” was necessary to improve the catalytic activity. Upon increasing the Rh loading on 15% La-doped ceria–zirconia support, the balance was built, i.e., CH₄ conversion increased from ~60 to 69% by increasing Rh loading from 0.1 to 0.5 wt% and only 2% conversion was elevated by doubling the Rh loading from 0.5 to 1.0 wt%.     

Influence of Indium Content on the Properties of Pt–Re/Al2O3 Naphtha Reforming Catalysts

The influence of indium on the properties of Pt–Re/Al₂O₃ catalysts used in naphtha reforming is studied. The addition of indium to the Pt–Re/Al₂O₃ catalyst produces a big decrease of acidity. It also produces an inhibition of the metal function, i.e., dehydrogenation and hydrogenolysis activity. The reaction of n-C₅ isomerization shows that indium addition decreases the total activity of the Pt–Re catalyst but increases the selectivity to the i-C₅ isomers. The selectivity to low cost light gases (C₁–C₃) is particularly decreased. The reaction of n-C₇ reforming showed that addition of indium increases the stability of the catalyst and the selectivity to aromatics, and decreases the production of light gases.     

The Effect of Copper Substitution on La2Ni1−x Cu x O4 Catalysts Activity for Simultaneous Removal of NOx and Diesel Soot

A series of the La₂Ni_1?x Cu _x O₄ (0 ≤ x ≤ 1.0) perovskite-like complex oxide catalysts, prepared and characterized by XRD, H₂-TPR, O₂-TPD and XPS, and catalytic activity tests, proved to be effective in the simultaneous removal of NOx and soot. The results indicated that the catalysts show the single orthorhombic K₂NiF₄-like phase. The doping of Cu led to the increase of orthorhombic distortion and the decrease of capability to accommodate non-stoichiometric oxygen, as well as the increase of the reducibility of lattice oxygen, resulting in improving catalytic activities. The La₂Ni_0.4Cu_0.6O₄ catalyst showed the highest activity. The maximum conversion of nitrogen oxide to molecular nitrogen was 15.6% and the ignition temperature decreased from 440 to 246 °C, as compared with the uncatalyzed soot combustion reaction.     

Ethanol Steam Reforming for Hydrogen Production over Bimetallic Pt–Ni/Al2O3

Ethanol steam reforming was studied at 673–823 K over Pt–Ni/δ-Al₂O₃. Results indicate that bimetallic catalyst is resistant to coke deposition at steam-to-carbon ratios as low as 1.5 and higher ratios are beneficial for both ethanol conversion and hydrogen formation. About 773 K is the optimum since high H₂ production rates are accompanied by low CO and CH₄ production rates. A power-function rate expression obtained on the basis of intrinsic rates at 673 K gives reaction orders of 1.25 (±0.05) and −0.215 (±0.015) for ethanol and steam, respectively; the apparent activation energy is calculated as 39.3 (±2) kJ mol⁻¹ between 673 and 723 K.     

Hydrogen Production by Methanol Steam Reforming Over Pd/ZrO2�CTiO2 Catalysts

Pd/ZrO₂?CTiO₂ catalysts were synthesized by sol?Cgel method and studied on the steam reforming of methanol reaction for hydrogen production. X-ray diffraction patterns of the Pd supported on single oxides showed crystalline structures associated with the zirconia or titania respectively. However, the XRD pattern of the mixed ZrO₂?CTiO₂ oxide showed broad diffraction pattern consistent with an amorphous material. The reducibility of the PdO supported on single and mixed oxides showed a negative peak associated with the desorption of H₂ due to the decomposition of Pd-hydride (PdH); as well as, positive peaks related with the hydrogen consumption on the reduction of the PdO supported. Catalytic activity on the palladium supported on the mixed ZrO₂?CTiO₂ oxide showed higher catalytic activity than the Pd supported on the single TiO₂ or ZrO₂ oxides. This finding was associated at the higher Pd species present in the Pd/ZrO₂?CTiO₂ than on the Pd/ZrO₂ or Pd/TiO₂ catalysts how was observed by TPR.     

Effect of Metal-Support Interactions in Ni/ZSM-5 + Al2O3 Catalysts on the Transformation of n-Paraffins

NiO(8 %)/Ni,H-ZSM-5 + Al₂O₃ (1:1) catalysts differing in metal-support interactions, which influenced the metal-to-acid ratios, were examined. The interactions were changed by modifying the method of zeolite and aluminium hydroxide combining and the method of Ni incorporation. The catalysts were characterised by ICP, XRD, N₂ sorption, SEM, TEM, NH₃-TPD, Py-IR, TPR, H₂ chemisorption and XPS. The effect of metal-support interactions was determined during n-C₆ conversion in a continuous system at H₂:CH = 7:1 Nm³/m³, 0.1 MPa and LHSV = 1 h^?1. It was found that over the catalysts with weaker Ni–alumina interactions (n _{Ni_a}/n, 3.2 × 10^?2 and 4.8 × 10^?2), selectivity to isomerisation products was by 10–35 % higher, and selectivity to high boiling hydrocarbons by 10–30 % lower than over the catalysts with stronger Ni-support interactions (n _{Ni_a}/n, 1.2 × 10^?2 and 1.8 × 10^?2).     

Kinetics of Oxidative Steam Reforming of Ethanol Over Bimetallic Catalysts Supported on CeO2–SiO2: A Comparative Study

Topics in Catalysis - The catalytic activity of M(Ag, Ru, Pt)–Ni/CeO2–SiO2 catalysts prepared by wet impregnation at different M loadings (0–3 wt%) for oxidative steam...     

Effect of fluorine and CaO/Al2O3 mass ratio on the viscosity and structure of CaO–Al2O3-based mold fluxes

The effect of CaO/Al₂O₃ mass ratio (C/A) and fluorine content on the viscosity and structure of CaO–Al₂O₃-based mold fluxes has been researched in this paper. The viscosity results indicated that increasing fluorine only slightly decreases the viscosity of the slag melt, and higher C/A is also observed to decrease the viscosity of molten slag when the C/A changes from 1.3 to 1.7. Structural analysis of the as-quenched fluxes using the Raman spectroscopy showed that the amounts of Al–O⁰ and Si–O–Al structural units all decrease with higher fluorine content and C/A, indicating that a depolymerization of the molten structure is occurring. The results of ²⁷Al and ¹⁹F magic angle spinning nuclear magnetic resonance showed that fluorine tends to participate in the network structure and coordinate with Al³⁺ ions to form complex ionic clusters. The results suggested that the role of fluorine in the CaO–Al₂O₃-based slag system is different from the traditional slag system in which fluorine only acts as a diluent, thus reducing the effect of fluorine on lowering the viscosity. In addition, the coordination environment of Al³⁺ ions can be simplified by higher C/A through promoting the generation of [AlO₄]⁻ tetrahedral structures. Besides, the free O²⁻ ions provided by excess CaO would break the Al–O⁰ bonds and further depolymerize the network structure, thereby decrease the viscosity.     

Effect of steam content and O2 pretreatment on the catalytic activities of Au/CeO2–Fe2O3 catalysts for steam reforming of methanol

The Au/CeO₂–Fe₂O₃ prepared by deposition–precipitation were studied by steam reforming of methanol at a reaction temperature range of 200–400 °C. Complete methanol conversion was obtained at the optimal steam/methanol ratio of 2 at 400 °C. A high steam content strongly depressed both methanol conversion and hydrogen concentration since this led to a complex mechanism and the formation of carbonate and formate species. After pretreating with oxygen, the catalytic activity dramatically decreased with the presence of an inhomogeneous Ce_xFe_1−xO₂ solid solution phase; the covering Au sites by the free α-Fe₂O₃ particles; and an agglomeration of both free α-Fe₂O₃ and Au particles.