Nickel-loaded catalysts

Fig. 3 (curves a and b) shows results obtained with a lower COj/CH ratio of two. It can be seen that the higher nickel loaded catalyst (4% Ni/ZrOJ also lost activity under these conditions. The catalyst with the lowest loading of nickel (1. WoNi/ZrOj) was stable under these conditions and showed no weight loss on TGA/DSC analysis. Fig. 3 (curve c) gives the results for the 1,1% Ni/Zr02 catalyst obtained with a C(VCH4 ratio of unity. The TGA/DSC experiment on this sample showed that there was some carbon deposition (2% weight loss). 

Fig. 5 shows the effect of various supports of nickel-loaded catalysts and reaction temperature on the methane conversion, in the partial oxidation of methane. At methane to oxygen ratio of 5 1, the maximum conversion of methane is 40 %, when reaction (5) proceeded, and 10% when complete oxidation proceeded. Only the oxidized diamond-supported Ni catalyst exceeded 10% conversion above 550 C, indicating that the synthesis gas formation proceeded. Ni-loaded LazOz catalyst afforded considerable methane conversion above 450 °C, but the product is mainly COz. Other supports to nickel showed no or only slight catalytic activity in the partial oxidation of methane. These results clearly show that oxidized diamond has excellent properties in the partial oxidation of methane at a low temperature, giving synthesis gas. Fig. 6 shows the effect of temperature on the product distribution, in the partial oxidation of methane. Above 550 °C, Hz and CO were produced, and below 500 °C, only complete oxidation occurred. The Hz to CO ratio should be 2 according to the stoichiometry. However, 3.2 and 2.8 were obtained at 550 and 600 °C, respectively. 

A dependence of the amount of carbon deposition on the nickel loading was observed forNi/Al203 catalysts (197). For example, a l-wt% Ni/Al203 exhibited much less carbon deposition than a 13.6 wt% Ni/Al203 catalyst (197). 

The cross-coupling of 3-iodopyridine and 4-dimethylamino-phenylacetylene was reported to work efficiently in the presence of a nickel based catalyst system too (7.42.),60 The described conditions (e.g. catalyst loading, solvent, temperature, additive) are more or less the same as in the conventional palladium catalyzed variant, although the nickel based system gave only poor results with bromoazines. 

The present work reports on results of the liquid-phase catalytic hydrogenation of butynediol on supported nickel catalysts specifically tailored for these processes. In this respect, we have studied support effects, the influence of nickel loading as well as the influence of Cu as a second metal. 

XPS measurements demonstrated that loaded Ni is predominantly located between the layeres of the catalyst and little remains on the external surface.15) For sensitivity reasons, a sample with 1 wt% Ni-loading was used. Comparison of the Ni2p3/2 peak intensity in the catalyst with that in a reference sample (which was also 1% Ni-loaded KNb03 with almost the same BET surface area as that of K4Nb6017) has shown that the surface concentration of Ni in the former is about 100 times less than that of the reference sampled EXAFS spectra for 1 wt% Ni-loaded samples both before and after the reduction procedure, as well as for Ni and NiO as standards, indicated that after reduction by H2 at 500°C for 2 b the loaded Ni was completely reduced to the metallic state.15) Even after reoxidation by 02 at 200°C for 1 h, most of the Ni remained metallic. (By XPS, the Ni, which remained on the external surface, was found to be in the oxidized form.) The formation of metallic nickel on a 0.1 wt% Ni-loaded catalyst was also confirmed by ESR measurements.7 The appearance of an intense resonance line after the reduction and reoxidation indicates the formation of ferromagnetic metallic nickel in the sample. 

The route of catalyst deactivation via a cyclic metal impregnation and deactivation method has produced significant improvements in approaching realistic vanadium and nickel profiles over the catalyst particles. From electron microprobe analyses of Ni and V loaded catalyst it has been established that after pore volume saturation, Ni and V are rather homogeneously distributed over the catalyst. 

Figure 1 Effect of nickel loading on stability of catalysts for C02 reforming CtyCH4= 4.

Catalyst Nickel loading (wt. %) Average particle size (A) Reaction temp. (°C) Turnover number (sec"1 x 103) Reference... 

Catalytic Activity of Nickel-Loaded Titanates. A good test of the dispersion of the active metal is the activity and selectivity for the hydrogenolysis of n-butane. For example, it is well known (6) that the hydrogenolysis of saturated hydrocarbons, or the rupture of carbon-carbon bonds by hydrogen, are structure sensitive that is, their rates per surface metal atom (TOF s) vary with the percentage of metal exposed on the catalyst (i.e.. the dispersion). Typically,... 

Comparative tests have been performed in the semi-batch reactor system to evaluate the Ru/Ti02 cataly versus a more conventional nickel-based catalyst. These tests show that rutlienium at only 3% metal loading has about the same activity as nickel at S0% metal loading. This comparison is only for short-term activity of the catalyst. As demonstrated in the continuous flow tests, the nickel catalyst loses activity readily in tlie first hours on stream, while the ruthenium maintains its activity. 

Supported Nickel. - The interaction of nickel with siUca and alumina at various stages of catalyst preparation has been extensively studied and only some recent evidence for interaction and its effect on performance are noted here. Nickel nitrate impregnated on silica decomposed to NiO during calcination, which interacted little with the support, whereas the ESCA spectrum of low nickel loadings on 7-alumina were quite different and NiO only appeared once the surface sites were filled. After reduction at 673 K and examination by ESCA without exposure to air, it was shown that percentage reduction depended on both Ni content and calcination temperature, which was considered indicative of a strong interaction between nickel and alumina. Nickel ions in octahedral sites are readily reduced and increasing the calcination temperature makes them diffuse to tetrahedral sites where they are difficult to reduce. 

Besides pyridine-containing polystyrene and pol)q5ropylene resins, polybenzimidazole has been employed as support for nickel(II) acetylacetonate [94]. The nickel-loaded polymer was shown to be an efficient catalyst for the epoxidation of (S)-(—)-limonene, a-pinene, and 1-octene using isobutyraldehyde/02 as coreac-tant/oxidant. However, significant metal leaching from the support associated with a loss of activity upon recycling was reported. It was shown that the reaction is heterogeneously catalyzed, and leached metal species did not contribute to the catal)d ic activity. 

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