Metal catalyst pretreatment temperature

Peterson and Scarrah 165) reported the transesterification of rapeseed oil by methanol in the presence of alkaline earth metal oxides and alkali metal carbonates at 333-336 K. They found that although MgO was not active for the transesterification reaction, CaO showed activity, which was enhanced by the addition of MgO. In contrast, Leclercq et al. 166) showed that the methanolysis of rapeseed oil could be carried out with MgO, although its activity depends strongly on the pretreatment temperature of this oxide. Thus, with MgO pre-treated at 823 K and a methanol to oil molar ratio of 75 at methanol reflux, a conversion of 37% with 97% selectivity to methyl esters was achieved after 1 h in a batch reactor. The authors 166) showed that the order of activity was Ba(OH)2 > MgO > NaCsX zeolite >MgAl mixed oxide. With the most active catalyst (Ba(OH)2), 81% oil conversion, with 97% selectivity to methyl esters after 1 h in a batch reactor was achieved. Gryglewicz 167) also showed that the transesterification of rapeseed oil with methanol could be catalyzed effectively by basic alkaline earth metal compounds such as calcium oxide, calcium methoxide, and barium hydroxide. Barium hydroxide was the most active catalyst, giving conversions of 75% after 30 min in a batch reactor. Calcium methoxide showed an intermediate activity, and CaO was the least active catalyst nevertheless, 95% conversion could be achieved after 2.5 h in a batch reactor. MgO and Ca(OH)2 showed no catalytic activity for rapeseed oil methanolysis. However, the transesterification reaction rate could be enhanced by the use of ultrasound as well as by introduction of an appropriate co-solvent such as THF to increase methanol solubility in the phase containing the rapeseed oil. 

Nitroalkanols are intermediate compounds of /1-amino alcohols that are used extensively in many important syntheses. They are obtained by Henry s reaction through the condensation of nitroalkanes with aldehydes. Different nitro compounds have been reacted with carbonyl compounds in reactions catalysed by alkaline earth metal oxides and hydroxides/621 Among the catalysts examined, MgO, CaO, Ba(OH)2, and Sr(OH)2, exhibited high activity for the reaction of nitromethane with propionaldehyde. The yields were between 60 % (for MgO) and 26 % [for Sr(OH)2] at 313 K after 1 h in a batch reactor. The study of the influence of the pretreatment temperature of the solid showed that for MgO and CaO a... 

Conjugate addition of methanol to a,jS-unsaturated carbonyl compounds forms a new carbon-oxygen bond to yield valuable ethers. Kabashima et al.[70] reported the conjugate addition of methanol to 3-buten-2-one on alkaline oxides, hydroxides and carbonates at a temperature of 273 K. The activities of the catalyst follow the order alkaline earth metal oxides > alkaline earth metal hydroxides > alkaline earth metal carbonates. All alkaline earth metal oxides exhibited high catalytic activities. The yields obtained after 10 min in a batch reactor with MgO, CaO or SrO exceeded 92 %, whereas with BaO the yield was lower (72 %), probably because of its low surface area (2m2g ). As observed for other reactions, the catalytic activity of MgO strongly depends on the pretreatment temperature. 

Perimeter interface around metallic particles appears to be the most important part in the metal catalysts active at low temperatures. For Pt/Sn02, Pt-Sn alloy formation (thus, reducing pretreatment) is crucial for the enhancement in catalytic activity, while for Au/Ti02, oxidic Au formation (thus, oxidizing pretreatment) is assumed to be crucial. 

Catalytic CO oxidation has lately drawn considerable attention due to the growing applications for air purification, pollution control in automobiles, and incinerator exhaust gases. In addition to many different metal oxide catalysts, a wide variety of precious metal catalysts have been studied for low-temperature CO oxidation. Among them, it is noteworthy that Au nanoparticles deposited on oxide supports, such as AI2O3, SiOz, TiOz, MnOx, FezOs, and NiO, are very active for CO oxidation at room temperature [1-4]. Although Pd/SnOz and Pt/SnOz were known to be active for the low-temperature oxidation of CO, they often required complicated pretreatments and relatively long induction periods [5-7]. A Pd/CeOz-TiOz catalyst was also recently reported to exhibit high catalytic activity for CO oxidation at low temperature [8]. 

Fig. 2 shows the conversion vs. temperature curves for H2 oxidation over Iridium catalysts pretreated by hydrogen reduction. Comparing the obtained conversions in H2 oxidation with those in CO oxidation, it was found that the temperatures for 50% conversion of H2 oxidation over Ir catalysts, except for IrA i02-DP, was similar to those in CO oxidation. Over Ir/Al203-DP and Ir/Fe203-DP catalysts, H2 oxidation proceeds at lower temperatures than CO oxidation. This feature is similar to those of other typical noble metal catalysts. It should be noted that CO oxidation over the Ir/Ti02 catalyst takes place at temperatures even below room temperature and at much lower temperature than H2 oxidation. This feature is the same as that of highly dispersed Au catalysts [1-4]. These results indicated that the support effect for the CO oxidation was much larger over Ir catalysts than that over Au catalysts. 

In this work the hydrogenolysis of ethyl laurate (EL) to dodecanol (ROH) and ethanol has been studied on different Ru-Sn/ALOs catalysts. Systematic studies have been made to investigate the influence of precursor compounds, sequence of impregnation, metal loading, Sn Ru atomic ratio, catalyst pretreatment (calcination, reduction) and reaction conditions (temperature, H2 pressure). The calcined catalysts were characterized by Ten erature Programmed Reduction (TPR). Correlation between the activity and TPR characteristics of Ru-Sn/Al203 catalysts was also demonstrated. 

Each of the prepared supported metal catalysts (40 mg) was pressed into self-supporting pellet of 20 mm in diameter, and was placed in an infrared cell, which was connected to an iso-volumetric system equipped with a vacuum line. The pressure of this system can be measured to the order of 1 x 10 Torr by a capacitance manometer. The catalysts were pretreated with O2 at 723 K for ten hours and then reduced under H2 at 723 K for ten hours, followed by evacuation at the same temperature for one hour before use. Adsorption of CO was carried out at 298 K. 

Both the metal particle size and the crystallite size of supported metal catalysts have decisive effects on enantioselectivity, but other parameters of the reaction often become important as well for example, the nature of the metal, the nature of the support, the method of preparation, the salt used for preparation, the mode of catalyst reduction, and the nature of catalyst pretreatment, such as high temperature heating or sintering. 

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