Catalysts Ni-based

Ni-based Catalysts. - Ni-based catalysts have been by far the most investigated catalysts for the CF formation via methane decomposition. This may be attributed to the high CF yield obtained on Ni-based catalysts. CF yield is defined as the total amount of CF formed per gram of catalyst at complete deactivation. Since the catalyst has to be essentially replaced for subsequent CF formation, from an economics point of view it is desirable to achieve extremely high CF yields. 

Several studies have been carried out aimed at synthesizing nickel-based catalysts in the most suitable form for providing high activity and better carbon resistance. Some of the nickel-based catalysts synthesized include bimetallic catalysts, oxide-supported Ni catalysts, Ni-based perovskites, and Ni core-shell structure catalysts, which are discussed in this section. 

MPa (300—400 psig), using a Ni-based catalyst. Temperatures up to 1000°C and pressures up to 3.79 MPa (550 psia) are used in an autothermal-type reformer, or secondary reformer, when the hydrogen is used for ammonia, or in some cases methanol, production. 

Linear dimeri2ation and oligomeri2ation of butadiene can be achieved by using a number of catalyst systems based on Pd, Ni (158—161), and Fe (162). 1,7-Octadiene can be obtained selectively when the dimeri2ation is carried out in the presence of a reducing agent such as formic acid (163—165) or H2/CO2 (166). 

In this work, the catalytic reforming of CH4 by CO2 over Ni based catalysts was investigated to develop a high performance anode catalyst for application in an internal reforming SOFC system. The prepared catalysts were characterized by N2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). 

The Ni based anode catalysts were prepared by a physical mixing method. NiO (99.99%, Sigma-Aldrich Co.), YSZ (TZ-8Y, TOSOH Co.), MgO (98%, Nakarai Chemical Co.) and Ce02 (99.9%, Sigma-Aldrich Co.) were used as raw materials. The physically mixed catalyst... 

The internal reforming of CH4 by CQzin SOFC system was performed over an ESC (electrolyte st rported cell) prepared with Ni based anode catalysts. Figure 5 diows the performance of voltage and power density with current density over various ESC (Ni based anodes I YSZ (LaSr)Mn03) at SOOC when CH4 and CO2 were used as reactants. To improve the contact between single cell and collector, different types of SOFC reactor were used [5]. In the optimized reactor (C), it was found fliat die opai-... 

In contrast to the Pt catalysts discussed above, Ni based catalysts (i.e., also when supported on ZrO usually form coke at such a rapid rate that most fixed bed reactors are completely blocked after a few minutes time on stream (see Fig. 8) [16], The coke formed with the Ni catalysts is filamentous. The Ni particle remaining at the tip of the filament hardly deactivates as the coke formed on its surface seems to be transported through the metal particle into the carbon fibre, but the drastic increase in volume causes reactor plugging and prevents use of the still active catalyst (see Fig. 8). The TEM photographs indicate that the carbon filaments have similar diameters to those of the Ni particles. 

Scheme 6.15) are other related processes that can be mentioned alongside the Heck reaction [73], In addition, Ni-based catalysts have also been reported [74],... 

Very recently Chen and co-workers have applied the previously mentioned Ni-based dimetallic pre-catalyst 14 in the Negishi reaction. Remarkable results were obtained even when unactivated aryl chlorides were chosen as reaction partners providing an alternative to the more expensive Pd-based catalysts. The fact that dinuclear pre-catalyst 14 is more active than its mononuclear analogue 13 indicates a possible cooperative effect between the two metal centres [86] (Scheme 6.23). 

Nickel (Ni)/Copper (Cu)/Zinc (Zn) Nickel exhibits a mixture of ferrous and nonferrous metal properties, and Ni-based alloys are characterized by corrosion resistance. Therefore, Ni has been widely used in stainless steel (about 65% of the Ni consumed in the Western World) and superalloys/nonferrous alloys (12%). Turbine blades, discs and other critical parts of jet engines and land-based combustion turbines are fabricated from superalloys and Ni-based superalloys. The remaining 23% of consumption is applied in alloy steels, rechargeable batteries, catalysts and other chemicals, coinage, foundry products, and plating (USGS, 2006). 

The contribution deals with the catalytic performance of V-, Co-, and Ni-based microporous (MFI), mesoporous (HMS) and alumina catalysts in ODH of ethane. Representative catalysts contained between 2.9 and 3.9 wt.% of metal. Ni-, V- and Co-A1203, and V- and Ni-HMS were effective catalysts in ODH of ethane. However, Ni-A1203 had the best selectivity-conversion behavior. The most favorable set up corresponded to 46 % in the ethane conversion, 30 % in the ethene yield 30 %, 65 % in the selectivity to ethene, and 0.91 g(C2=).gca, 1.h 1 in the ethene productivity for Ni-A1203. The activity was stable for 6 hours time-on-stream. 

Partial oxidation of methane to syngas over Ni and Co catalysts was effected by use of microwave irradiation, and compared with conventional heating [73]. Although the same conversion levels and H2/CO ratio (2.0 0.2) were observed, the temperature of the catalyst bed was much lower (200 K) when microwave irradiation was used than with conventional heating. Under both activation modes the Ni-based... 

The reaction mechanism of the SMR reaction strongly depends on the nature of the catalytically active metal and the support (the detailed discussion is provided in the review [14]). The kinetics and mechanism of the SMR reaction over Ni-based catalysts have been extensively studied by several research groups worldwide. For example, Xu and Froment [16] investigated the intrinsic kinetics of the reforming reaction over Ni/MgAl204 catalyst. They arrived at the reaction model based on the Langmuir-Hinshelwood reaction mechanism, which includes several reaction steps as follows ... 

H2 CO ratio in the resulting syngas is about 1.7. However, due to the relatively high content of CO in the syngas, carbon deposition may still be a problem, especially for Ni-based catalysts widely used for steam reforming. 

Partial oxidation is also mentioned as a process to convert ethanol to hydrogen.124 Another novel technology for ethanol to hydrogen has been described by Toci and Modica.125 It is based on cracking ethanol vapors by "cold-plasma-chemical processing" in the presence of a Ni-based catalyst. 

Catalysts for this codimerization reaction can be derived from prac-tially all the Group VIII transition metal compounds. Their catalytic properties, such as rate, efficiency, yield, selectivity, and stereoselectivity, vary from poor to amazingly good. Some better-known catalyst systems and their product distributions are listed in Table I. As one can see, the major codimerization product under the given condition is the linear 1 1 addition product, 1,4-hexadiene. The formation of this diene and its related C6 products will become the center of our discussions. The catalyst systems that have been investigated rather extensively are derived from Rh, Ni, Co, and Fe. We shall cover these systems in some detail. A lesser-known catalyst system based on Pd will also be briefly discussed. 

Kinetics. Although the SRE reaction has been studied over various noble metals-, and Ni-based catalysts, kinetic studies have been reported only for a few Ni-based catalysts. For Ni/Al203, Ni/Y203 and Ni/La203, Sun et al.41 have observed that the reaction was first order with respect to ethanol and employed the following rate equation ... 

Iron (Fe), 74 490-529. See also Fe entries Ferr- entries Iron compounds Ironmaking processes Manganese ferroalloys MoFe protein Nickel-chromium—iron alloys Nickel—iron-aluminum catalyst Ni-Fe-base alloys VFe protein... 

Ni-based reforming catalysts are pyrophoric they will sinter if exposed to air and they represent a fire hazard for consumers. 

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