Nickel catalysts standard procedures

This type of catalyst is not limited to nickel other examples are Raney-cobalt, Raney-copper and Raney-ruthenium. When dry, these catalysts are pyrophoric upon contact with air. Usually they are stored under water, which enables their use without risk. The pyrophoric character is due to the fact that the metal is highly dispersed, so in contact with oxygen fast oxidation takes place. Moreover, the metal contains hydrogen atoms and this adds to the pyrophoric nature. Besides the combustion of the metal also ignition of organic vapours present in the atmosphere can occur. Before start of the reaction it is a standard procedure to replace the water by organic solvents but care should be taken to exclude oxygen. Often alcohol is used. The water is decanted and the wet catalyst is washed repeatedly with alcohol. After several washes with absolute alcohol the last traces of water are removed. 

A novel nickel-aluminum-alumina catalyst was used in this work. The same catalyst was used in all tests although several different batches were prepared. Since a standardized procedure was used, variations in catalyst composition were not great and activity was reproducible. Because details of the preparation and composition are presented in several patent applications, no further discussion of the catalyst is given. 

A recent modification in the use of Raney nickel may greatly enhance its utility. Industrial use of the standard procedure has been limited by the necessity to use such large quantities of the very expensive Raney nickel. It now appears that the use of the nickel-aluminium alloy itself in formic acid leads to very efficient desulphurizations with Ni/S ratios of only 0 2. High proportions of the aluminium seem to give the best results, apparently because of the ability of the aluminium to regenerate the active nickel catalyst. Similar results were obtained using nickel or cobalt salts in the presence of auxiliary metals such as aluminium or iron. 

The chemical combination of nickel oxide and support explains the need for high-temperature reduction of nickel oxide/kieselgulu catalysts before use and the high metal content required (see Table 3.10). A practical solution to the problem was to prereduce the catalyst at a high temperature and to stabilize the reduced nickel with air before use in industrial reactors. By the 1930s prereduction and stabihzation were becoming standard procedures for catalysts used in fat-hardening and iso-octane operations. 

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 second well-documented research area that involved zero-valent nickel-catalyzed carboxylation was initiated by Dunach et al. during the 1990s [58a-c], These studies showed that electrochemically generated Ni(0)- and Mg(II)-based species represented good alternatives to the catalysts used in standard synthetic procedures. The formation of unsaturated carboxylic acids was proposed as a catalytic reaction initiated by Ni(0), although the exact mechanism and the obligatory... 

Catalyst Characterization. Chemical analyses, x-ray diifraction analyses, and gas adsorption procedures were used to characterize the composition, crystallographic character, and surface structure of the nickel and cobalt zeolite catalyst preparations. The chemical and x-ray procedures were standard methods with the latter described elsewhere 11). Carbon monoxide chemisorption measurements provide useful estimates of the surface covered by nickel atoms from the zeolite substrate 10). 

The performance of several of the nickel and cobalt zeolite catalysts for steam reforming of n-hexane at 400°-500°C has been evaluated by short test runs with the reactor and the procedures described above (Table II). A Girdler reforming catalyst (G56) was tested under the same conditions as a comparative standard. All tests were conducted at a total pressure of 1 atm. Plateaus of sustained reforming activity were established within 1 hour. The cobalt catalysts lost essentially all reforming activity within 3 hours, presumably because of oxidation by steam. The space velocities reported are calculated in terms of theoretical hydrogen production based on the n-hexane injection rate and extent of conversion (Equation 2, Table II). The equation for the steam reforming of n-hexane with complete conversion to carbon dioxide is... 

---