Catalytic activities of metals

Contaminant coke is produced by catalytic activity of metals such as nickel, vanadium, and by deactivation of the catalyst caused by organic nitrogen. 

In order that the possibility of contamination of catalysts with traces of oxides could be eliminated Campbell and Emmett (51) studied the catalytic activity of metallic films of nickel and its alloys with copper or gold. They were deposited under a high vacuum and then sintered (alloys also homogenized) in hydrogen at 5 cm Hg pressure at 350°C or 500°C. The films were subsequently allowed to cool to room temperature and only... 

As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCl4, ZrCU, HfCU), catalytic efficiency for the alkylation decrea.ses in the following order hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride... 

Correlation Between Catalytic Activity of Metals and Their Bulk Properties... 

Summarizing the discussion above, we can only say that all the relations observed experimentally between the parameters of catalytic activity of metals and parameters of their physicochemical bulk properties are secondary. The primary factor influencing the catalytic activity of all metals and most of their physicochemical parameters are... 

Fig. 1. Catalytic activities of metals for ethane hydrogenolysis in relation to the percentage d character of the metallic bond. The closed points represent activities compared at a temperature of 205°C and ethane and hydrogen pressures of 0.030 and 0.20 atm, respectively, and the open points represent percentage d character. Three separate fields are shown in the figure to distinguish the metals in the different long periods of the periodic table.

Fig. 4. Catalytic activities of metals (as potentials measured at 10-4 A.cm-2) for anodic oxidation of different reductants. Er thermodynamic oxidation-reduction potentials of reductants. H2 reversible hydrogen electrode potential in solution used to study oxidation of each reductant. Adapted from ref. 38.

Because of a great practical importance of SMR as a major industrial process for manufacturing H2, the development of efficient steam reforming catalysts is a very active area of research. Nickel and noble metals are known to be catalytically active metals in the SMR process. The relative catalytic activity of metals in the SMR reaction (at 550°C, 0.1 MPa and steam/carbon ratio of 4) is as follows [12] ... 

Tomita, K., Studies on the formation of polyethylene terephthalate 6. Catalytic activity of metal compounds in polycondensation of bis(hydroxyethyl)terephthalate, Polymer, 17, 221-224 (1976). 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

The following general points may be made about the catalytic activity of metals for the exchange of hydrocarbons ... 

Effects of Complexing on Catalytic Activity of Metal Ions... 

Some evidence to support this scheme has been obtained. Thus the catalytic activity of metals has been found to be associated with the formation of soluble metal-thiol complexes (13), and the geometric configuration of thiols has been found to affect the over-all rate of oxidation,... 

As described above, the catalytic activity of metal ion-exchanged zeolites for aniline formation has a good correlation with electronegativity and with the formation constant of ammine complexes of metal cations. The order of the activity agrees with the Irving-Williams order. These facts give irrefutable evidence that the transition metal cations are the active centers of the reaction. 

Catalytic activity of metal ions coordinated to the framework of mesoporous molecular sieves atracted attention at first. Recently, catalytic activity of the metal ions incorporated into extraffamework positions of the MCM-41 in various reactions was also reported [3], But, the site geometry, coordination and distribution of the metal ions in the extraframework sites of the MCM-41 host matrix are not understood, and only a few papers have dealt with this problem. For dehydrated Mn-(A1)MCM-41, only one type of single cation was reported [4],... 

Table 16.4 Comparison of the specific catalytic activity of metals,12,15 carbides and oxides12,15 in the reaction of hydrogen oxidation at 623 K, 22 kPa H2, 2.8 kPa Oz...

The importance, for catalytic activity, of metal sites exhibiting different coordination environments has been evaluated by using asymmetrically coordinated dinuclear species [103b]. A mixture of l,4,7-trimethyl-l,4,7-triazacyclono-nane (Me3tacn) and bpy yielded bis(p-oxo)p-carboxylato) [Me3(tacn)MnmMnIV (bpy)], 54, the first such complex. This was indeed catalytically active, but still at the same low level (105 slower than catalase) as other symmetrical models. Nevertheless, the requirement for two metals for catalysis was confirmed since decomposition of the dinuclear species yields inactive, but similarly coordinated mononuclear complexes. 

This section describes a simple model that enables evaluation of the influence of charge effects on the catalytic activity of metallic nanostructures. Also, the results of experiments performed with nanostructured catalysts synthesized by laser electrodispersion are discussed. These results demonstrate a relationship between the catalytic activity and charge density in the... 

The brief review emphasizes the useful catalytic activities of metal oxides, i.e., Ru02, towards 02-evolution but points to their limitations as a result of surface recombination with intermediate H-atoms. Possible routes to circumvent these difficulties could involve elimination of surface H-atom through the application of homogeneous H2-evolution catalysts (see Sect. 4.3), and compartmentalization of the oxidation catalyst from the H2-evolution catalyst, i.e., liposomes. Alternatively, reduction of other substrates rather than water i.e. C02, could lead to intermediate carbonous species being insensitive to oxidation by intermediate O-species. 

Metals frequently used as catalysts are Fe, Ru, Pt, Pd, Ni, Ag, Cu, W, Mn, and Cr and some of their alloys and intermetallic compounds, such as Pt-Ir, Pt-Re, and Pt-Sn [5], These metals are applied as catalysts because of their ability to chemisorb atoms, given an important function of these metals is to atomize molecules, such as H2, 02, N2, and CO, and supply the produced atoms to other reactants and reaction intermediates [3], The heat of chemisorption in transition metals increases from right to left in the periodic table. Consequently, since the catalytic activity of metallic catalysts is connected with their ability to chemisorb atoms, the catalytic activity should increase from right to left [4], A Balandin volcano plot (see Figure 2.7) [3] indicates apeak of maximum catalytic activity for metals located in the middle of the periodic table. This effect occurs because of the action of two competing effects. On the one hand, the increase of the catalytic activity with the heat of chemisorption, and on the other the increase of the time of residence of a molecule on the surface because of the increase of the adsorption energy, decrease the catalytic activity since the desorption of these molecules is necessary to liberate the active sites and continue the catalytic process. As a result of the action of both effects, the catalytic activity has a peak (see Figure 2.7). 

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