Catalyst doping

Dehydration of 1-pentanol or 2-pentanol to the corresponding olefins has been accompHshed, in high purity and yields, by vapor-phase heterogeneous catalyzed processes using a variety of catalysts including neutral gamma —Al Og catalyst doped with an alkah metal (23), zinc aluminate (24,25), hthiated clays (26), Ca2(P0 2 montmorillonite clays (28). Dehydration of 2-methyl-1-butanol occurs over zinc aluminate catalyst at... 

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

The performance of the catalysts doped with transition metals on 20 mol% NiO/Ti02 catalyst for hydrogen production at 998 K and GHSV of 2700 h" at steady state. 

The enantioselective hydrogenation of a,p-unsaturated acids or esters, using 5wt% Pt/Al203 or Pd/Al203 commercial catalysts doped with cinchonidine (CD), was deeply investigated to evidence the specific activity of Pd or Pt and the role of the reaction parameters and solvent polarity. Finally, the steric and electronic effects of different substituent groups were also studied. 

Figure 5. TGA comparison of standard and catalyst doped Li-Mg-B-N-H multinary complex hydride...

Fig. 2.4. Effects of noble-metal catalyst doping on the tin oxide (a) SpiU-over mechanism, (b) Fermi-level mechanism...

In another study, Ni-based catalysts doped with small amounts of transition metals (Ni (11.8 mol%)/M (2.9 mol%)/MgO/Al203, where M = Fe, Co, Mo) showed high H2 selectivities for ATR of i-Cg compared to a Ni/Mg0/Al203 catalyst (see Table Results suggest that the addition of a small amount... 

Figure 4 shows the CTL spectra for catalysts doped with various activators. The peak wavelength of the CTL spectrum for the activated catalyst corresponds to the electronic transition from the ground state to the excited state of the activator. 

Fig. 4 CTL spectra for catalysts doped with various activators...

We have recently76 carried out further work on the effect of the addition of various promoters to a coprecipitate having a Ni/Al ratio of 2.5. We chose to use 1.2 mol% of these additives, this quantity having given the most significant decrease in the activity of such catalysts doped with sodium.60 It was found that the group I cations all had a detrimental effect on the activity of the catalysts, the effect increasing in the order ... 

For various types of catalyst there are results of kinetic investigations for the oxidative dehydrogenation of ethane available (e.g., for a magnesium oxide catalyst doped with samarium oxide, lithium nitrate and ammonium chloride [64] or a V2O5/Y-AI2O3 catalyst [68]). In another study with a Sn.oLai.oNdi.oOx catalyst, investigations were reported of noncatalytic reactions, which were found to be significant at temperatures above 700 °C [69]. 

Another study on the use of Fe showed that the oxidation rate of acetaldehyde was improved with Ti02 catalysts doped with Fe and Si s)mthesized by thermal plasma (Oh et al., 2003). A Fe content lower than 15% rendered higher activities than the untreated catalyst. The catalyst preparation technique involved a complex procedure using a plasma torch, with all this likely leading to an expensive photocatalyst of mild prospects for large-scale applications. 

The selectivity decreased for catalysts doped with cesium, palladium, ruthenium, zinc, and zirconium. The influence of these metals was thought to be an indication of the role of these metals in promoting the overoxidation of MA to carbon oxides. However, molybdenum was found to poison the overoxidation reaction. 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

A number of other groups have also found that zirconium enhances the activity of vanadium phosphate catalysts [11, 56, 146, 148, 150, 154, 156-163]. Zeyss and coworkers [158] investigated catalysts doped with 5 to 15% zirconium. Unlike the... 

Nickel - molybdenum - alumina catalysts doped with fluoride and/or lithium, AlChE Symp. Ser, Tar Sand and Oil Upgrading, (eds S S. Shih and c.M- Oballa) (submitted for publication). 

Ethane and propane Ni/Al203-Ce02 700-900 1.5 Ni/Al203 catalyst doped with 14% Ce02 showed the best performance. Laosiripojana et al.111... 

Another problem is the formation of methanol over the LTS catalyst. The methanol accumulates in the process condensate and in the gas entering the CO2 removal system.Therefore, emissions from the plant can become an environmental concern. Catalysts doped with Cs have been developed to address this problem. These catalysts reduce the production of methanol by nearly 90%. 

Recently, oxidative coupling of methane has been studied in order to utilize natural gas as a chemical carbon source. Various materials (ref. 1-12) have been reported to be effective catalysts. However, roles of the catalysts have not been studied well. Ito, Lunsford et al. have reported that an active catalyst has a radical center (for example (Li 0 J) under the reaction condition (ref. 3-a, b, c). Although this must be an essential factor, it seems difficult to explain the effectiveness of such a variety of catalyst materials by one factor. In this study we tried to abstract the important factors to determine the apparent activity and selectivity of this reaction by using MgO catalysts doped with various metal oxides. 

Fukuda and Kusama [11] successfidly partially hydrogenated butynediol by enq>loying Pd-CaCOj and quinoline as poison. In later work of Fukuda [3], the combination effect of lead acetate and quinoline on Pd/BaCOs gave partial hydrogenation as weU. hi order to selectively produce m-butenediol, Chaudhari et al. [12] reported the use of Lindlar catalyst doped with zinc acetate that gave partial reduction with selectivity as high as 99.8% toward m-butenedioL... 

FIGURE 141 Above Activity of Cr/silica-titania (5 wt% Ti02) catalysts doped with varying amounts of sodium or lithium formate, then activated at 650 °C and tested at 107 °C. Below Melt indices of polymers made with the catalysts described above. 

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