Selective Hydrogenation of Citral Over Noble Metals Intercalated Montmorillonite Catalysts

Surfactant stabilized platinum and ruthenium nano particles were intercalated into the interlamellar space of montmorillonite. The XRD patterns of the metal intercalated montmorillonite reveal that there was a significant swelling during the intercalation of surfactant stabilized metal particles without affecting the crystallinity of montmorillonite. The success of the synthesis of nano particles into montmorillonite catalysts was confirmed from the TEM micrographs of the catalytic materials. The TEM micrographs clearly indicated well dispersion of particles and the average diameter (in nm) of the intercalated metal particles were also determined. The catalytic activity and selectivity of these newly developed catalysts towards the selective hydrogenation of citral in liquid phase was found to be appreciable. The conversion levels were found to be 38% and 18% at 30 °C and increased to 61% and 46% at 100 °C over Pt-CTA-MM 2 and Ru-CTA-MM 2 catalysts respectively at 9 bar hydrogen pressure. The best selectivity towards geraniol and nerol was observed to be 61% over Pt-CTA-MM 2 among the catalysts studied. The effect of temperature, hydrogen pressure, amount of catalyst and time on stream on the conversion and selectivity towards geraniol and nerol were also discussed in detail.     

Hydrodechlorination Reactions of CCl4 Over HZSM-5- and HY-Supported Pt and Pd Catalysts

The hydrodechlorination reactions of CCl₄ have been studied over Pt/HZSM-5, Pt/HY, Pd/HZSM-5 and Pd/HY under hydrogen atmosphere in the 393?C673?K temperature range in a pulse microreactor. The catalysts were prepared by impregnation and were characterised by various physico-chemical means. It has been found that all catalysts were active in the partial to full dechlorination reactions. Typically, over the Pt-containing catalysts methane was the major dechlorinated product, while it was ethane over the Pd-containing catalysts. This latter product predominated over the Pd/HZSM-5 and the quantities of the di- and trichlorinated products were minimal and the monochlorinated one was not formed at all. Phosgene formed was the indication of the partial destruction of the support being more serious for the HY-supported ones.     

Effect of Pt Particle Size and Phosphorous Addition on Furfural Hydrogenation Over Pt/Al2O3

Catalysis Letters - Pt/Al2O3 catalysts with different Pt particle sizes and after phosphorous deposition were studied for liquid phase catalysed furfural hydrogenation. The activity and selectivity...     

The Oxidation of Methane at Low Temperatures Over Zirconia-Supported Pd,Ir and Pt Catalysts and Deactivation by Sulfur Poisoning

Abstract  

The oxidation of methane over zirconia-supported Pd, Ir, and Pt catalysts at low temperatures under an oxidizing atmosphere and the effect of SO₂ on this reaction were investigated. An Ir–Pt/ZrO₂ catalyst exhibited high activity and low deactivation by SO₂. Characterization of the catalyst indicated the presence of a highly oxidized Pt species that was stabilized by the addition of Ir.     

Oxidation Reactions over Multi-Component Catalysts: Low-Temperature CO Oxidation and the Total Oxidation of CH4

A series of NM/MO _x /Al₂O₃ (NM = Pd, Ag, Pt, and Au) catalysts were prepared and tested in the oxidation of CO and CH₄. The catalysts were characterized with X-ray diffraction and transmission electron microscopy. Where addition of MO _x generally does not seem to affect the catalyst activity in CH₄ oxidation, a large enhancement in CO oxidation was observed. Fourier transform infrared spectroscopy has been used to identify the role of MO _x as a promoter for low-temperature CO oxidation. The results were found to support a Mars and van Krevelen type model.     

负载型贵金属催化剂在甲醛完全催化氧化上应用的研究进展

甲醛是一种主要室内空气污染物之一,其对人体的健康造成很大的危害。催化氧化法是一种有效治理甲醛的方法。负载型贵金属催化剂因其在室温下就可以对甲醛具有很强的催化氧化能力,所以被认为是治理甲醛的最有前景的催化材料。因此,文章的目的是介绍贵金属催化剂在治理甲醛方面的研究进展。最后对负载型贵金属催化剂在甲醛催化氧化上的应用进行展望。     

Exhaust Gas Catalysts for Heavy-Duty Applications: Influence of the Pd Particle Size and Particle Size Distribution on the Combustion of Natural Gas and Biogas

In this study, an experimental investigation concerning exhaust gas catalysts for heavy-duty diesel engines fuelled by natural gas or biogas is presented. Miniature monoliths, 2.5 wt% Pd/Al₂O₃, have been prepared, characterised and tested. Various methods have been used in order to obtain different palladium particle sizes, including incipient wetness and microemulsion technique. Crystallite sizes between 2 and 40 nm were obtained. We observed that the metal particle size influences the activity for methane oxidation. Moreover, the homogeneity of the active material was found to affect the reaction rate.     

Comparison of Ethylene Glycol Steam Reforming Over Pt and NiPt Catalysts on Various Supports

Steam reforming of ethylene glycol (EG) was studied on Pt and NiPt catalysts supported on γ-Al₂O₃, TiO₂, and carbon. On all supports bimetallic NiPt catalysts show higher activity for H₂ production than the corresponding Pt catalysts as predicted from model surface science studies. The kinetic trends are similar for all catalysts (Pt and NiPt) with the H₂ production rate being zero-order and fractional order with respect to water and ethylene glycol, respectively. Slight differences in selectivity to minor products are observed depending both on active metal and support. On γ-Al₂O₃, NiPt shows higher H₂ and less alkane formation than Pt. TiO₂ supported catalysts show increased water-gas shift activity but also increased selectivity to alkane precursors. NiPt/C is identified as an active and selective catalyst for EG reforming.     

Thermal Stable Pd/Ce0.2Y0.8O2-δ Catalysts for CO and CH4 Oxidation

A series of Pd/Ce_0.2Y_0.8O_2-δ catalysts were prepared and tested for CO and CH₄ oxidation. It is found that the Pd/Ce_0.2Y_0.8O_2-δ catalysts are thermal stable, and the catalytic activity enhances with increasing calcination temperature. The enhancement of the activity is due to the decomposition of surface carbonate species and the increase in average oxidation state of Pd.     

Effect of Particle Size on Monometallic and Bimetallic (Au,Pd)/C on the Liquid Phase Oxidation of Glycerol

The influence of metal particle size of monometallic and bimetallic supported catalysts (Au, Pd, Au–Pd)/C was studied using as a model reaction the liquid phase oxidation of glycerol. By tuning the metal particle size from 2 to 16 nm a progressive decrease of activity and simultaneously an increase in the selectivity to sodium glycerate was observed. Moreover, the influence of the temperature was studied and it was found that by increasing the temperature, only with a large particle size the formed glycerate was retained and not over-oxidized to tartronate.     

Effect of Pt Dispersion on the Catalytic Activity of Supported Pt Catalysts for Diesel Hydrocarbon Oxidation

The catalytic activity of Pt/Al₂O₃ for the total oxidation of hydrocarbon mixture of n-decane and 1-methylnaphthalene was strongly dependent on the Pt dispersion. The maximum hydrocarbon oxidation activity was achieved for Pt/Al₂O₃ with Pt dispersion (D_Pt) of 0.39. On the other hand, the activity of Pt/ZrO₂ monotonously decreased with decreasing Pt dispersion from 1.00 to 0.09. In situ FT-IR spectroscopy suggested that the presence of plural Pt species in metallic state with slight different electric state, which well catalyze the formation of acrylate species as an intermediate, is responsible for the high catalytic activity of Pt/Al₂O₃ with D_Pt = 0.39.     

Particle Size, Particle Size Distribution, and Related Measurements of Supported Metal Catalysts

It should be apparent from the contents of this review that no single method provides a full characterization of particle size and/or particle size distribution in supported metal catalysts without some inherent theoretical shortcoming, experimental difficulty, or ambiguities in interpretation of results. The message is clearly to use more than one technique whenever possible in order to obtain intercomparisons both of size/size distribution number themselves and internal consistency of the data. However, to be avoided are incorrect comparisons, such as sizes obtained from the Scherrer formula and chemisorption experiments, for example, which measure different things. We believe that high-resolution TEM has a bright future in catalyst characterization, but perhaps the most accessible and convenient combination at present is that of Fourier line profile x-ray analysis and chemisorption, albeit at the expense of some analysis in the former case.     

Hydrogenation of But-1-yne and But-1-ene on Palladium Catalysts: Particle Size Effect

The hydrogenation of but-1-yne and but-1-ene was studied on highly (D = 97%) and lowly (D = 26%) dispersed palladium on alumina catalysts. The activity calculated in terms of accessible palladium atoms was found to depend on the particle size. For the hydrogenation of but-1-ene, the turnover number was higher on highly dispersed catalysts than on the lowly dispersed one. The reverse was true for the hydrogenation of but-1-yne. During the hydrogenation of but-1-yne the quantity of but-1-ene produced without further hydrogenation was higher on small particles. A study by X-ray photoemission spectroscopy showed an increase of the binding energy by 1 eV for the 3d core level of palladium in 0.2% Pd/Al₂O₃ (D > 80%) , either before or after a catalytic run (no coalescence occurred). The catalytic results were interpreted as being due to the variation of the adsorption strength of the hydrocarbons. The unsaturated hydrocarbons could be more strongly adsorbed on very small palladium particles which may be considered as “electron deficient”. A calculation showed that the sticking coefficient of but-1-yne was at least 2.5 times as high on small particles as on larger ones.