Amorphous catalyst preparation

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. 

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

Along with hydrophobicity, large amounts of both water (to promote hydrolysis) and methanol employed as co-solvent in the catalyst preparation (to promote homogeneity) are needed to ensure optimal reactivity, showing the number of experimental parameters of the sol-gel synthesis which can be controlled independently to optimize the performance of the resulting catalyst. Finally, in contrast to zeolites and other crystalline porous materials, amorphous sol-gel materials show a distribution of porosity which does not restrict the scope of application of sol gel catalysts to substrates under a threshold molecular size. 

Figure 1.9 TG, DTG, and DTA profiles for an amorphous catalyst precursor obtained by coprecipitation of Fe(N03)3 and Mg(N03)2 in solution [65], This precursor is heated at high temperatures to produce a MgFe204 spinel, used for the selective oxidation of styrene. The thermal analysis reported here points to four stages in this transformation, namely, the losses of adsorbed and crystal water at 110 and 220°C, respectively, the decomposition and dehydroxylation of the precursor into a mixed oxide at 390°C, and the formation of the MgFe204 spinel at 640°C. Information such as this is central in the design of preparation procedures for catalysts. (Reproduced with permission from Elsevier.)...

Apopinenene, hydrogenation over amorphous palladium alloys catalyst preparation methods and, 36 358-... 

Tab. 3.S. Performance of sonochemically prepared amorphous catalysts in the aerobic oxidation of cyclohexanes (Equation 3.33).

Figure 6. HRTEM images of the activated catalyst prepared from H3PO4, showing (a) [100] projected (V0)2P207, (b) VOPO4 at the edge of (V0)2P207 crystallite and (c) amorphous region (indicated by the arrow) in (V0)2P207 crystallite.

The same authors compared catalysts prepared from these precursors and [Ru(BINAP)Cl2]2 adsorbed on MCM-41 (with 26 and 37 A pores) and an amorphous mesoporous silica (with 68 A pores) all treated with combinations of SiPh2Cl2 and Si(CH2)3X (X = NH2, CO2H). Catalysts were also prepared in which the organometallic precursors were immobilized by entrapment into silica (using sol-gel techniques). This is one of the few studies in which the performance of chiral phosphine catalysts immobilized by covalent and noncovalent procedures are compared directly. The materials were examined as catalysts for the hydrogenation of sodium a-acetamidocinnamate and of a-acetamidocinnamic acid under similar conditions to those used for the catalysts on unmodified MCM-41. The catalysts... 

Our emphasis here is not on catalyst preparation and structure, but we need to describe briefly the preparation and properties of several major catalysts amorphous silica, y-alumina, zeolites, activated carbon, and supported metals. 

In industrial procedures catalyst preparation in organic solvents is preferred, producing a more amorphous precursor with high density of active sites.1022 In addition, phosphorous compounds are usually injected into the feed to replenish phosphorous lost through hydrolysis. In this way an appropriate surface phosphorous vanadium ratio is maintained ensuring prolonged catalytic activity and selectivity. 

Amorphous polymers prepared by aluminum catalysts had an additional quartet at 6.40, 6.58, 6.64, and 6.74 ppm. The intensity of this quartet varied depending on the nature of the amorphous polymer, and roughly paralleled the content of head-to-head and tail-to-tail linkages determined by chemical means. Thus, this quartet was assigned to a tail-to-tail dyad. 

When one component of a bimetallic alloy is leached out, a finely divided metal powder of high surface area results. One of the oldest of these so-called skeletal metal catalysts is Raney nickel10,11. Nickel boride is a more recently developed hydrogenation catalyst prepared by the reduction of nickel salts with sodium borohydride12-14. Bimetallic catalysts are often used to achieve selective saturation of a double bond in bifunctional unsaturated systems, e.g. in dienes. Amorphous metal alloys, a newly developed class of metal catalysts15,16, have also been applied in the hydrogenation of alkenes and dienes. 

A highly dispersed Pd on ZrC>2 catalyst was prepared by activating an amorphous Pd35Zr65 alloy by oxidation at 543 K. Almost complete conversion in the hydrogenation of cyclohexene (523 K, hydrogen/cyclohexene = 9) was achieved with the catalyst prepared by a 10-h oxidation207. The conversion with the as-received sample was only... 

Armbruster, E., Baiker, A., Baris, H., Guenfherodt, H.J., Schlogl, R. and Walz, B. (1986) Ammonia synthesis over a novel catalyst prepared from an amorphous hennonacontaironnonazirconium precursor./. Chem. Soc., Chem. Commun., 299. 

All the metallic nanostructures deposited by laser electrodispersion on both types of silicon substrates were found to be exceedingly active in the above processes. The activity was orders of magnitude higher than that of typical supported catalysts prepared by the standard techniques. Such a high activity is presumably due not only to the small size and amorphous state of nanoparticles, but also to the influence exerted by the charge effects discussed above. 

Specific surface areas of the Al203 catalysts were much smaller than those of the oxides without the sulfate treatment, as shown in Table VIII. These catalysts were prepared from the crystallized oxides, and highly active catalysts were obtained by the treatment on the crystallized oxide rather than on the amorphous one. It is considered that the large difference in the surface area before and after treatment is brought about by the different method of catalyst preparation (140). 

As is shown in Figure 1, the production rates of the major hydrocarbons were kept constant for the amorphous catalyst. However, the crystalline FegoZrio catalyst which was prepared by heating the amorphous catalyst at 5608C for 20 hrs didn t approach any steady activity, as is shown in Figure 2. 

HTO Catalyst Preparation. Hydrous titanium oxide ion exchangers are amorphous inorganic compounds synthesized in the form of salts of weak acids represented by the empirical formula C(TixOyHz)n, where C is an exchangeable cation. HTO catalysts can be prepared by a technique that consists of synthesis of sodium hydrous titanate ion exchange material followed by exchanging active metal ions for the sodium. The synthesis involves three steps ... 

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