Metal deposition on catalysts

The most important undesired metallic impurities are nickel and vanadium, present in porphyrinic structures that originate from plants and are predominantly found in the heavy residues. In addition, iron may be present due to corrosion in storage tanks. These metals deposit on catalysts and give rise to enhanced carbon deposition (nickel in particular). Vanadium has a deleterious effect on the lattice structure of zeolites used in fluid catalytic cracking. A host of other elements may also be present. Hydrodemetallization is strictly speaking not a catalytic process, because the metallic elements remain in the form of sulfides on the catalyst. Decomposition of the porphyrinic structures is a relatively rapid reaction and as a result it occurs mainly in the front end of the catalyst bed, and at the outside of the catalyst particles. 

Effects of Metal Deposits on Catalyst Intrinsic Activity... 

The effects of metal deposition on catalyst pore plugging were not included in this computation of Wei and Wei (1982). Rather, this model... 

Moreover, the structure destruction of EAH-USY by metals was found to be related to the valence state of the metal ions. As shown in Figure 8, the higher the valence of metal ions, the more serious the structural effect of these metals. This might be explained either by the repulsive force between metal ions or the difficulty of diffusion of low valence metal ions in zeolite inner chaimels due to their large radius. In commercial RFCC units, it is useful to alleviate metal contamination by controlling the excess oxygen concentration in regenerator in order to keep the metals deposited on catalysts in a low valence state. 

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

As discussed in Chapter 2, nickel, vanadium, and sodium are the metal compounds usually present in the FCC feedstock. These metals deposit on the catalyst, thus poisoning the catalyst active sites. Some of the options available to refiners for reducing the effect of metals on catalyst activity are as follows ... 

When studying the electrochemical promotion behaviour of catalytic oxidations on metals deposited on YSZ, one always makes the same observation Positive currents, i.e. O2 supply to the catalyst, cause NEMCA (electrophobic behaviour) only for high 02 to fuel (Pa/Pd) ratios in the gas phase. How can we explain this, at a first glance, counterintuitive but general observation ... 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Typically, the Pd species for Heck couplings are homogeneous catalysts, stabilized by air-sensitive ligands. They present economic and environmental problems regarding separation, regeneration and reuse. These difficulties can be diminished with heterogeneous catalysts that are more easily recoverable from the reaction mixture. As mentioned in Sect. 2.6, a catalyst consisting of palladium metal deposited on por-... 

Magnetic Resonance Studies of Metal Deposition on Hydrotreating Catalysts and Removal with Heteropolyacids... 

X-ray absorption spectroscopy can provide information concerning oxidation state and local structure of metals deposited on FGG catalysts and related supports, even at the several hundred ppm level. This information is valuable towards the understanding of catalyst deactivation and passivation mechanisms, and ultimately will lead to the development of new passivation routes. 

MitcbeU, B. Metal Contamination of Cracking Catalyst. 1. Synthetic Metals Deposition on Fresh Catalysts. Ind. Eng. Chem. Res. 19 (1980) 201-13. 

Catalytic hydrogenation of DHL by various catalysts such as bulk metals and metals deposited on the carbon, oxides and salts has been studied since the 70 s of the last century (3). The disadvantages of such catalysts are the low surface area and the high content of the noble metals, which result in their high cost price. 

A byproduct of vegetable oil transesterification to make biodiesel fuel, glycerol (GO) has captured our attention for several reasons, in aqueous medium, GO itself can be converted to value-added commodity products such as propylene glycol (PG), lactic acid (LA) and ethylene glycol (EG) in the presence of a metal catalyst at mild conditions (2-7). An array of metals deposited on various supports have been examined as catalysts for the above reaction (6, 7). 

Detailed examination of the chemical nature of the metal deposit on the catalyst has proved difficult because of the complexity and heterogeneity of... 

Retention of such oil components as Zn and the alkaline earth metals has been reported in relatively few instances. Deposits on the catalysts have not always been related to the amounts of these elements consumed in the operation. Analysis of deposits on catalysts originating from lubricants indicated that Ba, Ca, Zn, and P are present in the same proportion as given by the particular formulation of the oil employed for engine lubrication. The average retention of the amount of Zn passing over the catalysts of several test vehicles was reported as 3% (49). 

The problem of metal deposition on the hydrodesulfurization catalysts has generally been addressed using any one of three methods ... 

Analyses of Used Catalysts. The analyses of five used catalysts tested with 50% W. Kentucky SCT SRC are given in Table 3. The coke and iron depositions appear to be strongly dependent upon catalysts Harshaw 618X and HDS-1443 are high, but Amocat 1A and IB are low in coke deposition. Since surface area measurements can include contribution by contaminants (particularly coke), these values have no clearcut meaning. Besides the coke deposition, metal deposition on the catalysts contributes to the catalyst deactivation. 

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