Sulfur catalyst interaction

Definite correlation was found between the amount of exchangeable or mobile sulfur and the HDS activity. A deeper insight can be gained into the mechanism of the sulfur-catalyst interaction and of the catalytic conversion, on the basis of these data. 

Reviewing the tracer studies on the mechanism of catal3dic hydrodesulfu-risation, it can be concluded that at this time, a general mechanism for these reaction cannot be given. Possibly, it does not exist at all. It is well seen, however, that sulfur-catalyst interaction influences the catalysts behaviour substantially the activity, to a large extent, depends on the Smob/Sirr correlation, S-uptake affects the number of vacancies and consequently the value of the vacancy empty sites ratio. It was seen that H2S treatment affects the catalyst selectivity. There are a number of examples on this, mostly for HDS/hydrogenation selectivity ratio, not referred here. 

Sulfur tolerances of Cu- and H-mordenite zeolite catalysts prepared by ion-exchange were examined in a fixed-bed flow-reactor system. Rates of reduction of NO over HM or CuHM with C2H4 and CuNZA with C3H6 are decreased by SO2 included in the feed gas stream. Surface areas and sulfur contents of the deactivated catalysts, their TGA and TPSR patterns and observations by XPS and Raman suggest the formation of a sulfur species on the catalyst surface in the form of sulfate (SO/ ) which causes the loss of NO removal activity of the catalysts. Data from Cu K-edge absorption spectra suggest sulfur electrostatically interacts with Cu ions on the catalyst surface. 

Augustine et al. working at atmospheric pressure observed that presulfiding has a profound effect on both the quantity and the quality of the carbonaceous overlayer formed during n-hexane conversion reactions, and the effects are greater for bimetallic samples than for Pt monometallic catalysts. Carbon is decreased in the presence of sulfur. The carbonaceous layer is more rich in hydrogen over the sulfided catalysts. They assumed that sulfur can interact with Lewis acid sites and thus deactivate sites for coking. 

Apesteguia, C.R., Brema, C.E., Garetto, T.F., Borgna, A., Parera, J.M. (1984). Sulfurization of Pt/AbOs-Cl Catalysts VI. Sulfur-Platinum Interaction Studied by Infrared Spectroscopy. Journal of Catalysis, Vol.89, No.l, (September 1984), p>p. 52-59, ISSN... 

HjS typically exists in much lower concentrations in Hj than CO or COj, but can have a deleterious effect on catalyst activity. Sulfur species are notorious catalyst poisons for dispersed metal catalysts because the unpaired electrons of sulfur strongly interact with the Pt surface, blocking sites needed for HOR. At anode potentials adsorbed HjS is rapidly converted into sulfur ad-atoms by the reaction in... 

R SiH and CH2= CHR interact with both PtL and PtL 1. Complexing or chelating ligands such as phosphines and sulfur complexes are exceUent inhibitors, but often form such stable complexes that they act as poisons and prevent cute even at elevated temperatures. Unsaturated organic compounds are preferred, such as acetylenic alcohols, acetylene dicarboxylates, maleates, fumarates, eneynes, and azo compounds (178—189). An alternative concept has been the encapsulation of the platinum catalysts with either cyclodextrin or in thermoplastics or siUcones (190—192). 

Vehicle data represents the complex interaction of many variables, including vehicle performance, reactor design and location, as well as catalyst properties. For a catalyst that has failed, one must ponder whether the converter design used in the vehicle is suitable for the catalyst, the quantity of the catalyst used is correct, the distance of the converter from the exhaust manifold is suitable, the catalyst has been inadvertantly overheated to above 2000°F or poisoned by lead and sulfur, or whether the catalyst can be modified to produce a far superior product. 

Another difference between diese catalysts is found in dieir functional group tolerance. Catalysts such as 12 are more robust to most functionalities (except sulfur and phosphorus), moisture, oxygen, and impurities, enabling them to easily polymerize dienes containing functional groups such as esters, alcohols, and ketones.9 On die other hand, catalyst 14 is more tolerant of sulfur-based functionalities.7 The researcher must choose die appropriate catalyst by considering the chemical interactions between monomer and catalyst as well as the reaction conditions needed. 

Rodriguez JA, Hrbek J (1999) Interaction of sulfur with well-defined metal and oxide surfaces Unravehng the mysteries behind catalyst poisoning and desulfurization. Acc Chem Res 32 719-728... 

After treatment at 373 K in helium flow, the coordination numbers of Mo-0, Mo-S and Mo-Mo were not largely different from those in the cluster 1 and the distances of Mo-0, Mo-S and Mo-Mo were hardly changed. After treatment at 573 K in He flow, however, the color of NaY changed from brown to black and the curve fitting results of the EXAFS data exhibited lower coordination numbers of all interactions than those of the cluster 1. The decrease in the coordination number seems to be not due to the decrease in sulfur amount in the catalyst but to the disordering of each interaction since the S/Mo ratio hardly decreased after thermal treatment. These results show that the structure of the cluster 1 loaded on NaY was maintained at 373 K, but lost at 573 K. 

This review deals with the transfer of an atom usually oxygen, occasionally sulfur from one species to another. Because the participants have closed electronic shells (they are octet-rule molecules for the most part), electronic interaction between them is not substantial. For that reason the intervention of a catalyst is nearly always required. 

For Pd-Ag membranes the manufacture of defect-free thin layers, reproducible in production, and stability are major issues. In addition, sulfur resistance and the interaction of the membrane with the catalyst material is important. 

Cheekatamarla and Lane [62, 63] studied the effect of the presence of Ni or Pd in addition to Pt in the formulation of catalysts for the ATR of synthetic diesel. For both metals, a promotional effect with respect to catalytic activity and sulfur poisoning resistance was found when either alumina or ceria was used as the support. Surface analysis of these formulations suggests that the enhanced stability is due to strong metal-metal and metal-support interactions in the catalyst. 

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