Influence of the crystalline structure of ZrO2 on the metallic properties of Pt in Pt/WO3–ZrO2 catalysts

The influence of the crystalline structure of ZrO₂ on the metallic properties of Pt, when supported on WO₃–ZrO₂, was studied. Pt supported on tetragonal zirconia loses its metallic properties while when supported on monoclinic zirconia it presents good metallic activities. WO₂,^2- deposited on amorphous Zr(OH)₄ before calcination generates an active material for n‐butane isomerization. The larger the fraction of the tetragonal phase of zirconia in this material, the higher the isomerization activity and the lower the metallic activity of Pt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Total Oxidation of Methane Over Sulfur Poisoning Resistant Pt/ZrO2 Catalyst: Effect of Pt2+–Pt4+ and Pt2+–Zr4+ Dipoles at Metal-Support Interface

Catalysis Letters - We present a Pt/ZrO2 catalyst that can operate in the harsh conditions of methane oxidation without being deactivated by SO2. XPS analysis of 1%Pt/ZrO2 catalyst revealed the...     

The function of zeolite on Pt autoreduction and dispersion in Pt/L and Pt/β catalysts

TPR, CO-FTIR and¹²⁹Xe NMR spectroscopic techniques were used to measure the distribution of platinum species after the calcination of Pt/L and Pt/ zeolites. Autoreduction which occurred in Pt/ zeolite was avoided in the channel of L zeolite. Pt particles dispersed well and exhibited excellent reactivity for the aromatization ofn-hexane in L zeolite.     

Preparation of Ti/Pt/SnO2–Sb2O4 electrodes for anodic oxidation of pharmaceutical drugs

Ti/Pt/SnO₂–Sb₂O₄ electrodes were prepared by alternating Sn and Sb electrodepositions, repeated 4 or 16 times, onto a platinized titanium foil by a thermo-electrochemical method. Chemical, electrochemical, and structural tests have been used for the characterization of Ti/Pt/SnO₂–Sb₂O₄ electrodes. Anodic oxidation of the aqueous solution contaminated by amoxicillin, clofibric acid, diclofenac, and ibuprofen having a concentration of 100 mg L^?1 and 0.035 M of Na₂SO₄ have been applied using Ti/Pt/SnO₂–Sb₂O₄ electrodes at a current density of 10 and 30 mA cm^?2. The chemical oxygen demand removals increased with current density and except for diclofenac, the Ti/Pt/SnO₂–Sb₂O₄ electrode with 4 electrodeposition repetitions gave the best results. The combustion efficiencies for diclofenac and ibuprofen were higher than those obtained with similar electrode material, prepared without platinization, especially in the assay run with Ti/Pt/SnO₂–Sb₂O₄ (16 electrodeposition repetitions).     

Nickel impregnated Pt/H-β and Pt/H-mordenite catalysts for hydroisomerization of n-hexane

Nickel impregnated Pt/H-β and Pt/H-MOR catalysts with different Ni content were prepared and subjected to hydroisomerization of n-hexane in the presence of flowing H₂ gas. The states of Pt and Ni were identified by ESCA. The particle size measured by TEM shows that average particle size increases with increasing Ni loading. The acidity of the catalysts was measured by TPD of ammonia. The catalytic activity of Ni containing and Ni free Pt/H-β and Pt/H-MOR catalysts was compared and found that addition of Ni up to a threshold value (0.3 wt% for β and 0.1 wt% for MOR) increases the n-hexane conversion and dimethyl butanes selectivity due to better metal-acid synergism and decreases the amount of cracked products. When the Ni amount exceeds the threshold values the conversion decreases and cracked products increase. Further the Ni impregnation of Pt containing acidic supports increases the sustainability of the catalysts and was found to favor the protonated cyclopropane (PCP) intermediate mechanism in n-hexane isomerization. β zeolite was found to be a better potential support than mordenite and the isomerized product mixture shows better octane number.     

Deep Oxidation of Benzene on Pt/V2O5–TiO2 Catalysts

The combustion of benzene was studied on Pt supported on V₂O₅–TiO₂ samples containing different amounts of V₂O₅. Vanadium was highly dispersed as V⁴⁺ for low V₂O₅ loadings, forming a vanadia monolayer on titanium dioxide for a V₂O₅ concentration of about 5%wt. V₂O₅–TiO₂ samples were more active than V₂O₅ and TiO₂ single oxides, and the activity increased with the vanadia content. The platinum dispersion in Pt/V₂O₅–TiO₂ catalysts increased with the V₂O₅ loading but the activity for the deep oxidation of benzene exhibited an opposite trend. Benzene combustion was a structure sensitivity reaction promoted on larger metallic Pt crystallites which were preferentially formed when the V₂O₅ content in the sample was decreased.     

Macroporous Monolithic Pt/γ-Al2O3 and K–Pt/γ-Al2O3 Catalysts Used for Preferential Oxidation of CO

Macro-porous monolithic γ-Al₂O₃ was prepared by using macro-porous polystyrene monolith foam as the template and alumina sol as the precursor. Platinum and potassium were loaded on the support by impregnation method. TG, XRD, N₂ adsorption–desorption, SEM, TEM, and TPR techniques were used for catalysts characterization, and the catalytic performance of macro-porous monolithic Pt/γ-Al₂O₃ and K–Pt/γ-Al₂O₃ catalysts were tested in hydrogen-rich stream for CO preferential oxidation (CO-PROX). SEM images show that the macropores in the macro-porous monolithic γ-Al₂O₃ are interconnected with the pore size in the range of 10 to 50 μm, and the monoliths possess hierarchical macro-meso(micro)-porous structure. The macro-porous monolithic catalysts, although they are less active intrinsically than the particle ones, exhibit higher CO conversion and higher O₂ to CO oxidation selectivity than particle catalysts at high reaction temperatures, which is proposed to be owing to its hierarchical macro-meso(micro) -porous structure. Adding potassium lead to marked improvement of the catalytic performance, owing to intrinsic activity and platinum dispersion increase resulted from K-doping. CO in hydrogen-rich gases can be removed to 10 ppm over monolithic K–Pt/γ-Al₂O₃ by CO-PROX.     

H2 and H2/CO oxidation mechanism on Pt/C, Ru/C and Pt–Ru/C electrocatalysts

The oxidation kinetics of H₂ and H₂ + 100 ppm CO were investigated on Pt, Ru and Pt–Ru electrocatalysts supported on a high-surface area carbon powder. The atomic ratios of Pt to Ru were 3, 1 and 0.33. XRD, TEM, EDS and XPS were used to characterize the electrocatalysts. When alloyed with ruthenium, a decrease in mean particle size and a modification of the platinum electronic structure were identified. Impedance measurements in H₂SO₄, at open circuit potential, indicated different mechanisms for hydrogen oxidation on Pt/C (Tafel–Volmer path) and Pt–Ru/C (Heyrowsky–Volmer path). These mechanisms also occur in the presence of CO. Best performances, both in H₂ and H₂ + CO, were achieved by the catalyst with the ratio Pt/Ru = 1. This is due to a compromise between the number of free sites and the presence of adsorbed water on the catalyst. For CO tolerance, an intrinsic mechanism not involving CO electroxidation was proposed. This mechanism derives from changes in the electronic structure of platinum when alloyed with ruthenium.     

Stability of Pt/γ-Al2O3 Catalysts in Model Biomass Solutions

The stability of a Pt/??-Al₂O₃ catalyst in liquid water and aqueous solutions of 5?wt% glycerol or sorbitol at 225?°C is examined using a variety of physicochemical methods. It is demonstrated that the presence of glycerol and sorbitol significantly reduces the hydration of ??-Al₂O₃ to form boehmite as compared to treatment in pure water. The stability against hydration increases with increasing carbon chain length. Treatment with polyol solutions also results in reduced agglomeration of supported metal particles. The prevention of boehmite formation and agglomeration of metal particles are attributed to the formation of carbonaceous species on the surface. In addition to these effects, the deposits block a considerable portion of active metal surface area. IR spectroscopic analysis indicates that dehydration reactions play an important role in the formation of the carbonaceous deposits. The present results illustrate that water and dissolved biomass compounds can strongly affect the stability of heterogeneous catalysts under reaction conditions.     

Simultaneous Removal of NO x and Soot Over Pt–Ba/Al2O3 and Pt–K/Al2O3 DPNR Catalysts

The effect of NO _x storage on the soot combustion activity when alkaline- and alkaline/earth-containing model DPNR catalysts are used is investigated in this work. The influence of different experimental conditions (NO concentration, temperature, and particulate loading) is addressed and discussed in relation to the NO _x storage efficiency and soot oxidation activity as well.     

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

Effect of Soot During Operation of a Pt–K/Al2O3 LNT Catalyst

The effect of soot on the NO _x storage-reduction performances of a Pt–K/Al₂O₃ catalyst is analysed in this work by performing lean-rich cycles at constant temperature. The interaction between soot and the stored NO _x has been also investigated by temperature programmed methods. It has been found that the presence of soot reduces the NO _x storage capacity of the catalyst; besides the presence of soot favours the decomposition of the stored nitrates. A direct reaction between the stored nitrates and soot is suggested, that has been explained on the basis of the surface mobility of the adsorbed nitrates.     

Thermal stability of Pt particles of Pt/Al2O3 catalysts prepared using microemulsion and catalytic activity in NO–CO reaction

Sintering behaviors of the Pt particles of Pt/Al₂O₃ catalyst prepared using different preparation methods (microemulsion, sol–gel, and impregnation methods) were investigated. It was found that the catalyst prepared by microemulsion had a higher resistance to sintering than did the sol–gel and impregnation catalysts. To limit the sintering even more, the catalysts were pressed. The resistance to sintering in all the catalysts was improved by pressing. The pressed microemulsion catalyst was little deactivated in the NO–CO reaction by thermal treatment at 700 °C for 12 h, and had a high activity relative to that of the sol–gel and impregnation catalysts.     

电感耦合等离子发射光谱法测定Pt/Al_2O_3催化剂中的Pt

用电感耦合等离子发射光谱法测定了Al2O3基催化剂中的Pt,考察了基体及所用试剂对Pt测定的影响,发现Al2O3基体、硫酸等对Pt测定均有负干扰,应在标准溶液与基体匹配的情况下进行测定。该方法的检出限为Pt0.10mg/L;样品的加标回收率96%以上。     

Pt/TiO_2光催化制氢的初步研究

对无氧条件下Pt/TiO_2光催化重整甲醇制氢的基本步骤进行简化,在同一体系中进行了光催化剂的合成和光催化制氢的两步反应。基于正交设计法对该复杂体系进行了分析,得到Pt载量、甲醇/水体积、灯距、前反应时间这4种影响因素的3个不同水平对放氢速率的影响。确定了最佳实验条件为Pt载量0.5％(mol)、甲醇/水体积比5:1、灯距12 cm、前反应时间3h。分析结果表明,Pt载量对放氢速率的影响最大。实验获得的最高放氢速率为5.84 ml·h~(-1)·g~(-1)。     

Loss of NOx storage capacity of Pt–Ba/Al2O3 catalysts due to incorporation of phosphorous

This work aims at determining the effect of the incorporation of P on NO_x storage capacity by NO_x storage-reduction (NSR) catalysts. Different amounts of phosphorous were deposited on a Pt–Ba/Al₂O₃ catalyst (1 wt% Pt and 17 wt% Ba) by impregnation of a phosphate salt. Samples were calcined at 723 K and characterized using X-ray diffraction (XRD), N₂ adsorption isotherms and X-ray photoelectron spectroscopy (XPS). Their NO_x storage capacity was also measured. It was observed that storage capacity decreased almost linearly with the P/Ba ratio and besides at a phosphorous concentration P/Ba ratio of <0.1 deterioration was low. At higher P concentrations (P/Ba ratio = 0.7) the NO_x storage was significantly reduced. It is proposed that the cause of the decline in NO_x retention capacity would be the formation of Ba–P phases (very likely Ba phosphates) at the expense of Ba carbonate or Ba oxide. These new phases would be unable to exchange NO_x.     

Pt/CeO2 catalysts in selective hydrogenation of crotonaldehyde: high performance of chlorine‐free catalysts

The hydrogenation of crotonaldehyde was conducted in gaseous phase, at atmospheric pressure, on Pt/CeO₂ catalysts prepared from metal precursors containing or not chlorine. The activities and selectivities were studied, at 253 K, as a function of the reduction temperature of the catalyst (473–993 K). The Pt/CeO₂ catalyst, prepared from tetraammineplatinum nitrate, led to 5–20% crotyl alcohol selectivity when the catalyst was reduced at low temperature (473–673 K), while increasing the reduction temperature up to 973 K, the crotyl alcohol selectivity reached more than 80%. Repeating a series of experiments after a re‐calcination treatment at 673 K, the selectivity decreased to only 40% after 473 K reduction to reach again more than 80% after 673 K reduction temperature. A phase transformation of Pt to CePt₅ was observed by XRD analysis after 973 K reduction treatment. Differently on Pt/CeO₂ catalysts containing chlorine, prepared from either chloroplatinic acid or tetraammineplatinum chloride, the crotyl alcohol selectivity never exceeded 30% and did not form alloy up to 973 K reduction temperature. The main results are interpreted considering that the activity of CePt₅ for C=C hydrogenation is low compared to unmodified platinum catalyst and the activation of the carbonyl bond is induced by the presence of oxygen vacancies sites located at the interface between ceria and the metallic particles. The results are in good accordance with the information known at the present time on the metal–support interactions in Pt deposited on CeO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pt掺杂TiO_2光催化CO_2/H_2O性能研究

用阳极氧化法制备TiO_2,光电沉积Pt进TiO_2中,考察掺杂前后TiO_2光催化CO_2/H_2O的效果。结果表明,掺杂Pt后TiO_2对光的吸收带边红移,提高了光响应电流,对CO_2/H_2O的催化能力更强,掺杂Pt后乙醇时空收率最高到9.15mg·(cm·h)~(-1),约是未掺杂的4.5倍。     

The effects of Cl-induced alloying in Pt–Sn/Al2O3 catalysts on butane/H2 reactions

The effects of oxidation/reduction regeneration treatments, with and without 1,2-dichloropropane present as a chlorinating agent, on the structure of Pt(3%)–Sn(4.5%)/Al₂O₃ catalysts have been correlated with selectivities for butane/H₂ reactions. Particles of Pt⁰ fin Cl-free catalysts were partly covered by Sn⁰, but retained exposed ensembles of Pt atoms which were active for isomerisation, hydrogenolysis and dehydrogenation reactions, the latter becoming dominant at high reaction temperatures. Coking reduced Pt ensemble size and, hence, also favoured high selectivities for dehydrogenation as hydrogenolysis and isomerisation sites became poisoned. In contrast, the addition of 1,2-dichloropropane in an oxychlorination step before reduction promoted 1:1 Pt⁰–Sn⁰ alloy formation after reduction, the proportion of the total Pt in alloy being enhanced by increasing 1,2-dichloropropane concentration and oxychlorination temperature. The alloy surfaces were inactive for isomerisation and hydrogenolysis reactions, giving dehydrogenation as the sole catalytic reaction.