Catalyst preparation precipitation

Preparation of palladium - calcium carbonate catalyst. Prepare 60 g. of precipitated calcium carbonate by mixing hot solutions of the appropriate quantities of A.R. calcium chloride and A.R. sodium carbonate. Suspend the calcium carbonate in water and add a solution containing 1 g. of palladium chloride. Warm the suspension until all the palladium is precipitated as the hydroxide upon the calcium carbonate, i.e., until the supernatant liquid is colourless. Wash several times with... 

The product is hydrogenated in 4,000 cc of ethanol at room temperature and under normal atmospheric pressure with a catalyst prepared In the usual manner from 400 g of Raney nickel alloy. The calculated amount of hydrogen is taken up in approximately 75 hours. After filtration and evaporation to a small volume, the residue Is distributed between 1,000 cc of chloroform and water each. The chloroform solution is then dried over sodium sulfate and evaporated to a small volume. Precipitation of the hydrogenation product with petroleum ether yields an amorphous white powder which Is filtered by suction, washed with petroleum ether and dried at 50°C In a high vacuum. 1. athyl-2-podophyllinic acid hydrazide is obtained in a practically quantitative yield. 

VOx supported on TiOi showed good catalytic activity in the selective oxidation of H2S to ammonium thiosulfate and elemental sulfur. V0x/Ti02 catalysts prepared by the precipitation-deposition method can achieve higher vanadium dispersions, and higher H2S conversions compared to those prepared by the impregnation method. 

The aurlchalclte mineral was calcined In air at 350°C for 4 hours according to the standard catalyst preparation procedure used earlier for the precipitated precursor (1 ). XRD showed that aurlchalclte and... 

In summary, large (>lpm) single crystal platelets of aurichalcite produced highly dispersed Cu and ZnO particles with dimensions on the order of 5 nm, as a result of standard catalyst preparation procedures used in the treatment of the precipitate precursors. The overall platelet dimensions were maintained throughout the preparation treatments, but the platelets became porous and polycrystalline to accommodate the changing chemical structure and density of the Cu and Zn components. The morphology of ZnO and Cu in the reduced catalysts appear to be completely determined by the crystallography of aurichalcite. 

As the metal particle size decreases the filament diameter should also decrease. It has been shown that the surface energy of thirmer filaments is larger and hence the filaments are less stable (11,17-18). Also the proportion of the Ni(l 11) planes, which readily cause carbon formation, is lower in smaller Ni particles (19). Therefore, even though the reasons are diverse, in practice the carbon filament formation ceases with catalysts containing smaller Ni particles. Consequently, well dispersed Ni catalysts prepared by deposition precipitation of Ni (average metal particle size below 2-3 nm) were stable for 50 hours on stream and exhibited no filamentous coke [16]. 

Figure 13. Specific 2-CP (open symbols) and 2,4-DCP (solid symbols) hydrodechlorination rate constant K) as a function of the average Ni particle diameter ( nO for reaction over Ni catalysts prepared via impregnation with nitrate (0,0), deposition-precipitation (A,A) and impregnation with nickel ethanediamine ( , ) r= 423K reaction data refer to aqueous solutions. (Reprinted from Reference [147], 2003, with permission from Royal Society of Chemistry).

In order to confirm the hypothesis made on the role of catalyst components, we carried out the reaction with a ratile-type V/Sb/0 catalyst, having V/Sb atomic ratio equal to 1/1 (Table 40.1). This catalyst was prepared with the conventional sluny method, and therefore had a surface area of 10 mVg, lower than that obtained with the Sn/V/Nb/Sb/0 catalysts prepared with the co-precipitation method. However, despite this difference, with V/Sb/0 the conversion of n-hexane was similar to that one obtained with Sn/V/Nb/Sb/0. This is shown in Figure 40.7, which reports the conversion of n-hexane, the selectivity to CO2, to / -containing compounds and the carbon balance as a function of the reaction temperature. 

The effect of Bi promotion for the selective oxidation of 1-octanol using H202 as oxidant is reported in Table 2. Since decomposition of H202 by Platinum Group Metals is rapid, H202 is fed continuously into the reactor over 2 hours. The results obtained demonstrate that the presence of Bi203 as an additive within the reaction mixture displays no significant influence on catalyst activity. However, Bi promoted Pt/C catalysts, prepared by co-precipitation of... 

In the last few years remarkable progress has been made in the preparation of supported metal catalysts. Entirely new methods have been developed, comprising precipitation of the metal as an insoluble salt or hydroxide on the support under controlled conditions, or loading the support with the metal by means of ion exchange. A feature of catalysts prepared according to the former method (I, 2) is that, after reduction, they have a high metal content (50% by weight, or more), while the metal crystals are still small (20-40 A) and distributed very uniformly over the support. The latter approach yields catalysts with metal crystallites of approximately 10 A however, the metal content is rather low [about 2% (3-5)]. 

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

Hua, Liu, and coworkers—impact of calcination pretreatment on Au/Fe203 catalysts. Hua and coworkers524 525 reported on the effect of calcination temperature on the water-gas shift rates of Au/Fe203 catalysts prepared by co-precipitation of HAuC14 and Fe(N03)3. Calcination temperatures utilized ranged from 200 °C to 600 °C. The impact of calcination temperature on the water-gas shift rate is shown in Table 126. 

The only solid acidic catalyst which has given high polymers at an appreciable rate at low temperatures, and which has been studied in some detail, is that described by Wichterle [41, 42]. This was prepared as follows A 10 per cent solution in hexane of aluminium tri-(s- or t-butoxide) was saturated with boron fluoride at room temperature, and excess boron fluoride was removed from the precipitate by pumping off about half the hexane. Two moles of boron fluoride were absorbed per atom of aluminium, and butene oligomers equivalent to two-thirds of the alkoxy groups were found in the solution the resulting solid had hardly any catalytic activity. When titanium tetrachloride was added to the suspension in hexane, an extremely active catalyst was formed but the supernatant liquid phase had no catalytic activity. The DP of the polymers formed by the catalyst prepared from the s-butoxide was much lower than that of polymers formed with a catalyst prepared from the r-butoxidc. 

Y. Z. Yuan, A. P. Kozlova, K. Asakura, H. L. Wan, K. Tsai, and Y. Iwasawa, Supported Au catalysts prepared from Au phosphine complexes and As-precipitated metal hydroxides Characterization and low-temperature CO oxidation, J. Catal. 170(1), 191-199 (1997). 

Pure alumina catalyst prepared either by hydrolysis of aluminum isopropoxide or by precipitation of aluminum nitrate with ammonia, and calcined at 600-800°, contains intrinsic acidic and basic sites, which participate in the dehydration of alcohols. The acidic sites are not of equal strength and the relatively strong sites can be neutralized by incorporating as little as 0.1 % by weight of sodium or potassium ions or by passing ammonia or organic bases, such as pyridine or piperidine, over the alumina. 

Anotlier example of dendritic POM complexes used as recoverable oxidation catalysts was reported by Plault et al. (SS). A series of ionic polyammonium dend-rimers containing between 1 and 6 POM units were prepared and used to catalyze the epoxidation of cyclooctene in a biphasic water/CDCls system. A comparison of the homogeneous mono-, bis-, tris-, and tetra(POM) catalysts indicated that there was no dendritic effect on the reaction kinetics within this series. However, a dendritic effect was found in the recovery of the catalysts. The dendritic catalysts were precipitated from the organic phase by addition of pentane. The recovery of the tri-and tetra-(POM) catalysts was easier (80—85% and 96%, respectively) than that of the mono(POM) catalyst. 

Supported Au catalysts have been extensively studied because of their unique activities for the low temperature oxidation of CO and epoxidation of propylene (1-5). The activity and selectivity of Au catalysts have been found to be very sensitive to the methods of catalyst preparation (i.e., choice of precursors and support materials, impregnation versus precipitation, calcination temperature, and reduction conditions) as well as reaction conditions (temperature, reactant concentration, pressure). (6-8) High CO oxidation activity was observed on Au crystallites with 2-4 nm in diameter supported on oxides prepared from precipitation-deposition. (9) A number of studies have revealed that Au° and Au" play an important role in the low temperature CO oxidation. (3,10) While Au° is essential for the catalyst activity, the Au° alone is not active for the reaction. The mechanism of CO oxidation on supported Au continues to be a subject of extensive interest to the catalysis community. 

For practical (real) catalyst systems, precipitation, ion exchange, impregnation and sol-gel processing procedures are used. In precipitation methods, a hydroxide or a carbonate of a metal may be precipitated from a solution of a metal salt onto the support material held in the solution. Thus, a copper-silica catalyst may be prepared using a Cu-nitrate solution in which silica is suspended. Additives of any alkali cause the precipitation of copper hydroxide onto the silica support. This is then dried and normally reduced in hydrogen at moderate temperatures ( 400-500 °C) to form the catalyst. In co-precipitation techniques , the support is precipitated simultaneously with the active catalyst. In the ion-exchange method, for example, highly dispersed Pt on... 

The activity of traditional ZnO-based catalysts may be improved by using new preparation methods. Cu-ZnO-Al203 catalysts prepared by a new oxalate gel precipitation exhibited higher activity in C02 reduction than did those made by coprecipitation, which was attributed to the isomorphous substitution of Cu and Zn.47 48... 

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