Nickel catalysts selectivity patterns

The selectivity pattern of catalysts prepared by using SnEt2Cl2 showed that the IPA/0IPA ratio has increased compared to that obtained on catalysts modified by tin tetraalkyls. Dn catalysts iMi-Snht-.lll., the selectivity of the formation of isopropanol decreased to. .. A - -..I.. Upon introducing tin from SnBz Cl the activity of the skeletal nickel catalyst slightly decreased. On this modified... 

It has been demonstrated that skeletal nickel catalysts can be modified with tin by using CSRs taking place between tin alkyls and hydrogen adsorbed on nickel. Upon applying this type of modification the selectivity pattern of the catalysts in the reductive ami-nation of acetone can be tailored. Selective poisoning of sites responsible for the formation of isopropanol could be achieved by using tin dibenzyl (or diethyl] dichloride as tin precursor compound. ... 

The natural material catalysts exhibit similar metal removal selectivity patterns as conventional hydrotreating catalysts. Vanadium removal activity is higher than that of nickel and overall activity increases with hydrogen pressure. Thus little change in intrinsic demetallation pathways is indicated with these materials. However, in contrast to CoMo/A1203, the nodule catalysts are only moderately active for HDS and essentially inactive for HDN. 

Fig. 4. Cyclohexene selectivity as a function of conversion in the cyclohexane oxidation at 450°C over nickel containing catalysts (a) influence of the metallic substrate A1 (Cl), Ti (C2) and Mg substrate (C3) as well as of the MO/AI2O3 catalyst (C7), respectively (b) influence of the pore length on the selectivity pattern.

Higher hydrocarbon molecules allow study of the unique cracking pattern of metals. These studies are usually carried out at low conversion to observe only primary hydrogenolysis. Nickel exhibits high selectivity to cleave terminal C—C bonds leading to demethylation that is, it cleaves only bonds that involve at least one primary carbon atom. For example, in the transformation of n-hexane, only methane and n-pentane are formed (180°C, Ni-on-silica catalyst, 0.3% conversion), whereas 2-methylpentane and 3-methylpentane yield methane, n-pentane, and isopentane.260 In the transformation of 2-methylpentane, the n-pentane isopentane ratio is close to 2, which corresponds to the statistical value. Under more forcing conditions, successive demethylations lead eventually to methane as the only product. 

Selective electroless nickel plating of particle arrays on polyelectrolyte multilayer was investigated for the potential applications in sensors, optoelectronics, and biochips.96 This process is based on the preparation of functional colloidal arrays on surfaces. In the next step metal deposition is carried out on the surfaces of the patterned particles secured on the substrate. Samples of colloidal arrays on patterned polyelectrolyte templates are first pretreated with a Pd(II)-based catalyst. After rinsing with deionized water and drying, samples were plated with nickel using dimethylamine borane (DMAB) as a reducing agent. Based on the results of this work,96 it was shown that the selective electroless nickel deposition on 3D patterned surfaces can be successful. 

The basic selectivity principles introduced for the reactions of nonactivated alkenes vide supra) are also valid for polar, activated alkenes such as alkyl acrylates. Whereas monosubstituted methylenecyclopropanes usually lead to the formation of product mixtures regardless of whether nickel(0) or palladium(0) is employed as catalyst, methylenecyclopropanes with (identical) geminal substituents usually give rise to only one major product and are thus especially useful for preparative syntheses. In this section general features of these reactions of substituted methylenecyclopropanes are exemplified for selected substituents and substitution patterns. 

Various other aromatic or aliphatic alkynes are likewise carbosilylated with a range of stereoselectivities, depending on the type and substitution pattern of the atkyne substrate 58. Nickel (e.g. NiCl2) catalysts are also active, however, with lower yields and selectivities. 

Table 3 presents data for the catalytic patterns of the samples Investigated in the m-xylene reaction. It is evident that m-xylene isomerization and disproportionation products typical of acidic catalysts appear when nitrogen is used as a carrier. This result indicates that the nickel-modification does not in principle change the reaction selectivity. The increase in the catalytic activity of the pure SAPO suggests that the introduction of nickel compounds during the hydrothermal synthesis of the SAPO-5 may effect the crystallization process, leading in this case to a catalyst with more expressed acidic properties. The selectivity remains... 

---