Metal deactivators, analysis

The long-term stability of the Ru/Ti02 catalyst was studied under various reaction conditions and the spent catalysts were characterized for assessing the reasons of deactivation. It was observed that the rate exhibits a rapid reduction at the initial several hours of reaction, followed by a slow and continuous deactivation. Analysis of the spent catalyst, by H2 adsorption after removing surface carbon, showed that the initial rapid reduction of activity is mainly due to metal sintering, while the continuous and slow deactivation is related to the occurrence of the SMSl phenomenon at the later part of the catalyst bed, where reducing conditions prevail. In order to avoid these processes which lead to catalyst deactivation, Ti02... 

There have been some examples of the use of LDMS applied to the analysis of compounds separated via TLC, although not specifically dealing with polymer additives [852]. Dewey and Finney [838] have described direct TLC-spectroscopy and TLC-LMMS as applied to the analysis of lubricating oil additives (phenolic and amine antioxidants, detergents, dispersants, viscosity index improvers, corrosion inhibitors and metal deactivators). Also a series of general organics and ionic surfactants were analysed by means of direct normal-phase HPTLC-LMMS [837]. Novak and Hercules [858] have... 

This coke has been related with feedstocks quality and more specifically with their carbon Conradson content. The catalyst used for this analysis was the sample without metals deactivated 20 hours, 30 cycles, and 80% steam. The MAT test was performed with feedstock of different quality gasoil, DMO, and mixture of gasoil-DMO. 

Jet fuels are aviation fuels used mainly by the United States and other North Atlantic Treaty Organization (NATO) nations for military establishments. Other fuels called Jet A and Jet A-1 are closely related fuels used by commercial airlines. JP are a complex mixture of primarily aliphatic (but also aromatic) hydrocarbons, derived from crude oil and/or kerosene by refining and adding various other additives such as fuel icing inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and static dissipaters. Gas chromatographic analysis of JP-8, the most recent JP, indicates that it is made up of complex mixture of 9 to 17 different hydrocarbons, including thousands of isomers and three to six performance additives. They are generally colorless liquids and smell like kerosene. 

As the crystal surface exposed to the atmosphere is usually not ideal, specific sites exist with even much lower co-ordination numbers. This is shown schematically in Fig. 3.5, which gives a model comprising so-called step, kink and terrace sites (Morrison, 1982). This analysis suggests that even pure metal surfaces contain a wide variety of active sites, which indeed has been confirmed by surface science studies. Nevertheless, catalytic surfaces often behave rather homogeneously. Later it will be discussed why this is the case. In short, the most active sites deactivate easiest and the poorest active sites do not contribute much to the catalytic activity, leaving the average activity sites to play the major role. 

The concept of continuous flow SILP hydroformylation was also tested in the biphasic, liquid-liquid hydroformylation of 1-octene using the Rh-norbos catalyst system [78], TOFs of 44 h"1 were achieved after 3-4 h with no sign of deactivation at prolonged reaction times. At steady-state conditions an n/iso ratio of 2.6 was obtained. No leaching of rhodium metal could be detected by ICP-AES analysis of product samples at least after these short reaction times. 

Effect of Noble Metal Addition to Ni-Based Catalysts. Unmodified Ni-based catalysts tend to deactivate rapidly due to both carbon deposition and sintering. As suggested by the thermodynamic analysis above, carbon formation can be significantly limited by the addition of steam, which can react with carbon by the reverse of reaction (8). Figure 12 shows typical results for such a catalyst, which contained 5.4 mg carbon per gram of catalyst after 54 h on stream. 

Based on this discussion, it is possible to clarify some aspects of the literature interpretations on the nature of the active species. Lunsford and coworkers [49, 93] published many papers indicating that the active species is colloidal palladium, which implies the easy dissolution of Pd in solution. An analysis of patents clearly reveals that this is not the case for active catalysts and various patents explicitly indicate that there is no leaching of Pd. On the other hand, a colloid would be difficult, if not impossible, to manage in a commercial process and its recovery would be not viable at the very low concentrations of dissolved metal employed. In addition, the presence of even traces of Pd in commercial H202 could be extremely dangerous in terms of the possibility of explosion. Finally, if the solid is a simple reservoir for Pd going into solution, a deactivation is expected with time-on-stream in continuous operations. 

A recapitulation of the catalyst stability data reported indicates that within the time scale of the hydrotreating runs, the UOP-filtered SRC filter feed gave relatively stable performance. SRC itself caused substantial catalyst deactivation Synthoil gave stable performance after an initial deactivation. Since dissolved metals and particulate matter are known to have an adverse effect on catalysts, a correlation was sought based on an analysis for these components. 

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