Catalysts coprecipitation

Tech. Data Sheet No. 7 , New York, Comml. Solvents Corp., 1968 The heat of adsorption of 2-nitropropane is very high, so carbon-containing respirators should not be used in high vapour concentrations. Also, if Hopcalite catalyst (coprecipitated copper(II) oxide and manganese (IV) oxide) is present in the respirator cartridge, ignition may occur. 

The catalytic properties of copper-chromium catalysts can be strongly affected by the presence of additives such as barium (3, 4). The selectivity however depends a great deal on the content and on the localisation of this promoter (4). Indeed we observed that the modification of a Cu-Cr/graphite catalyst by barium impregnation led to a different selectivity from the one obtained with a CuCrBa catalyst coprecipitated in contact with graphite (table S). 

Figure 7.8 XRD patterns of copper/zinc catalysts coprecipitated at pH 5 (PRs) and at pH 7 (PR7) from [32].

Chromia—alumina catalysts are prepared by impregnating T-alumina shapes with a solution of chromic acid, ammonium dichromate, or chromic nitrate, followed by gentie calciaation. Ziac and copper chromites are prepared by coprecipitation and ignition, or by thermal decomposition of ziac or copper chromates, or organic amine complexes thereof. Many catalysts have spiael-like stmctures (239—242). 

A variety of mixed metal catalysts, either as fused oxides (42 7 8) or coprecipitated on supports (25 0) or as physical mixtures of separate catalysts (5P), have been tested in aniline reductions. In the hydrogenation of ethyl p-aminobenzoate, a coprccipitated 3% Pd, 2% Rh-on-C proved superior to 5% Rh-on-C, inasmuch as hydrogenolysis to ethyl cyclohexanecarboxylate was less (61) (Table 1). 

One problem associated with the peroxotungstate-catalyzed epoxidation system described above is the separation of the catalyst after the completed reaction. To overcome this obstacle, efforts to prepare heterogeneous tungstate catalysts have been conducted. De Vos and coworkers employed W catalysts derived from sodium tungstate and layered double hydroxides (LDH - coprecipitated MgCU, AICI3, and NaOH) for the epoxidation of simple olefins and allyl alcohols with... 

On the basis of the experimental results, Sn02-Zr02 catalysts were prepared by the coprecipitation method. That is, Sn02 and Z1O2 were mixed chemically rather than physically. The effects of the Sn/Zr molar ratio and reaction temperature on the SO2 conversion and sulfur yield for Sn02-Zr02 catalysts were... 

By coprecipitating the catalytically active component and the support to give a mixture that is subsequently dried, calcined (heated in air), and reduced to yield a porous material with a high surface area. This procedure is followed when materials are cheap and obtaining the optimum catalytic activity per unit volume of catalyst is the main consideration. 

Fe/MgO catalysts with 5 to 30 mol % Fe have been prepared by impregnation and coprecipitation. Their reducibility has been measured and a comparison made of their Fe° surface areas. Catalysts prepared via coprecipitation yielded larger iron areas than those via impregnation. The activity and selectivity of the reduced catalysts for the hydrogenation of propanenitrile at 20-30 bar and 473 K and of ethanenitrile at 1 bar and 508 K have been determined. The most active catalysts are those prepared by coprecipitation and they show high selectivity for primary amines. The activity for ethanenitrile hydrogenation correlates with the iron surface area. 

Besides supported (transition) metal catalysts, structure sensitivity can also be observed with bare (oxidic) support materials, too. In 2003, Hinrichsen et al. [39] investigated methanol synthesis at 30 bar and 300 °C over differently prepared zinc oxides, namely by precipitation, coprecipitation with alumina, and thermolysis of zinc siloxide precursor. Particle sizes, as determined by N2 physisorpt-ion and XRD, varied from 261 nm for a commercial material to 7.0 nm for the thermolytically obtained material. Plotting the areal rates against BET surface areas (Figure 3) reveals enhanced activity for the low surface area zinc... 

Dining the last couple of years CdS-containing Nafion membranes have been apphed for the photocleavage of H2S . They are not comparable with the monograin membranes because the CdS particles are at randomly distributed in a rather thick Nafion membrane. This technique is attractive for some applications because the semiconductor particles are immobilized . On the other hand, problems may arise because of diffusion problems in the nafion membrane. Mainly the photoassistol Hj-formation at CdS was investigated in the presence of a Pt-catalyst and with coprecipitated ZnS CdS without a catalyst . 

Three series of Au nanoparticles on oxidic iron catalysts were prepared by coprecipitation, characterized by Au Mossbauer spectroscopy, and tested for their catalytic activity in the room-temperature oxidation of CO. Evidence was found that the most active catalyst comprises a combination of a noncrys-taUine and possibly hydrated gold oxyhydroxide, AUOOH XH2O, and poorly crystalhzed ferrihydrate, FeH0g-4H20 [421]. This work represents the first study to positively identify gold oxyhydroxide as an active phase for CO oxidation. Later, it was confirmed that the activity in CO2 production is related with the presence of-OH species on the support [422]. 

With nickel/alumina catalysts (cf. 4 ) preparation by coprecipitation or by the decomposition of a high dispersion of nickel hydroxide on fresh alumina hydrogel, yields nickel aluminate exclusively. On the other hand, when, as in impregnation, larger particles of nickel compound are deposited, the calcination product is a mixture of nickel oxide and nickel aluminate. The proportion of nickel oxide increases when occlusion of the impregnation solution leads to a very nonuniform distribution (49). 

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