Nickel-kieselguhr catalysts

Isomerization of sorbitol, D-mannitol, L-iditol, and dulcitol occurs in aqueous solution in the presence of hydrogen under pressure and a nickel—kieselguhr catalyst at 130—190°C (160). In the case of the first three, a quasiequiUbrium composition is obtained regardless of starting material. Equilibrium concentrations are 41.4% sorbitol, 31.5% D-mannitol, 26.5% L-iditol, and 0.6% dulcitol. In the presence of the same catalyst, the isohexides estabUsh an equihbrium at 220—240°C and 15.2 MPa (150 atm) of hydrogen pressure, having the composition 57% isoidide, 36% isosorbide, and 7% isomannide (161). 

Morikawa (100) and also Koizumi (101) found that the polymerization of ethylene proceeds rapidly in the presence of a nickel-kieselguhr catalyst containing 15% Ni, while both nickel or kieselguhr alone are extremely poor catalysts of this reaction. This might be interpreted by the presence of active sites localized at the interface of nickel and kieselguhr since the formation of a homogeneous new phase between these two components is improbable. 

In an effort to obtain a less temperature-sensitive system, lower nickel content catalysts were prepared on an alumina support and tested for demethylation activity. The first, Preparation A, with a nominal nickel content of 50 wt % was activated at 700°F in a slow stream of hydrogen at atmospheric pressure for 16 hours. This catalyst was tested at conditions similar to those employed with the nickel-kieselguhr catalyst reported above. The results are given in Table II. 

As may be seen from examination of these data, results are very similar to those obtained with the nickel-kieselguhr catalyst. The catalyst... 

Once near steady-state activity had been reached (19 hours), the temperature was decreased 15 °F, and the effect of decreased temperature on conversion and selectivity established, Run 4. An estimated activation energy for the conversion of methylcyclohexane is 28 kcal/mole, only 2 kcal less than the approximate value for the nickel-kieselguhr catalyst. The effect of decreased operating pressure is shown by the data of Run 5. Conversion increased, and efficiency to cyclohexane decreased slightly. The same effect was noted previously in fixed bed tests with Preparation A. 

A plot of In k" vs. 1/T for the nickel-kieselguhr catalysts is shown in Figure 2. The activation energy for the reaction is estimated at 30 kcal/mole. As mentioned earlier, this value was confirmed substantially by data taken during Period 4 of the fluidized-bed run (Table IV) where temperature control was better. In this run 28 kcal/mole was obtained despite the difference in catalyst composition. 

Copper can also be used as a catalyst, like nickel, alone, on carriers, or as a mixed catalyst with metals of the first to the eighth Group of the Periodic Table. The temperature needed for reduction of the catalyst, usually containing the copper as oxide, hydroxide, or basic carbonate, is 150-300°. Preparation of a copper-kieselguhr catalyst is similar to that of a nickel-kieselguhr catalyst.175... 

Nickel-kieselguhr catalysts with or without a small percentage of magnesia and thoria These catalysts were prepared by precipitation of the metals as carbonates from the solutions of their nitrates holding a suspension of B.D.H. kieselguhr. The carbonates were subsequently decomposed to the oxides in a current of air and the nickel reduced by hydrogen at 300°. 

A. Nickel-Kieselguhr Catalyst It was prepared by precipitating nickel carbonate from a hot solution of nickel nitrate by hot potassium carbonate solution in presence of kieselguhr, washing and drying the mass, and reducing it in situ in the reaction bomb itself by a stream of hydrogen at 300-350°. 

In Figure 3.15 are some experimental results of Kehoe and Butt [J.P.G. Kehoe and J.B. Butt, J. Appl. Chem. BiotechnoL, 23, (1972)] on the initial rates of the hydrogenation of benzene over a nickel-kieselguhr catalyst in an excess of hydrogen at low temperatures. Determine a consistent form of Langmuir-Hinshelwood expression to correlate these data, and obtain the values of the associated rate and equilibrium constants and their temperature dependence. 

Table 4.7. Rate of formation of (R)-(-)-MHB (mmol h g ) and ee values in the enantioselective hydrogenation of methyl acetoacetate on deposited nickel-kieselguhr catalysts, promoted with 1% noble metals and modified with (2R,3R)-tartaric acid (according to summarized data of Orito et al. ).

Fig. 6.11. Hydrogen isotherm on nickel-kieselguhr catalyst obtained from deuterium chromatography. Note Data points of 0 C and—20 C not shown. (Reproduced with permission by Suzuki, M. and Smith, M., J. Catai, 23, 325 (1971)).

Fig. 6.12. Effect of hydrogen pressure on exchange rate on nickel-kieselguhr catalyst.

The parent 7-oxanorbomane, 1, is commercially available. Its preparation starts with the catalytic hydrogenation of hydroquinone to generate a mixture of trans-and cfs-cyclohexane-l,4-diol [15-18]. cfs-Cyclohexane-l,4-diol can be isomerized into the more stable trans isomer with metallic sodium [17]. Dehydratation of the latter on A4 zeolites, on alumina [19], or over nickel-kieselguhr catalyst [20] provides 1. This reaction is exergonic (ArG° = ArH° — TArS° = -3.1 2.5 kcal/mol) at room temperature as its standard gas phase heat of reaction amounts to ArH° = -1-7.3 2.5 kcal/mol. A variation of entropy of reaction of ca. -1-35 eu is assumed for this fragmentation, what leads to —TArS° = 298(0.035) = — 10.4 kcal/mol. The standard gas phase heat of formation of frans-cyclohexane-1,4-diol (Scheme 1) is estimated from that of cyclohexanol (—69.0 2.0 kcal/mol) and the standard heat of oxidation of cyclohexane into cyclohexanol (—39.5 kcal/ mol) [21]. Chickos and Acree [22] give AfH°(l) = -43.4 0.5 kcal/mol (see also [23-25]). 

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