Noble metal chlorides

There are also catalysts that lack any apparent source of metal-carbon bonds. These catalysts include the aforementioned alumina- and silica-sup-ported transition metal oxides (which, in principle, do not demand any activation by organometallic compounds), and also several group 6-8 transition metal chlorides (soluble in hydrocarbons or chlorohydrocarbons), most typically RuC13. Some of these transition metal halides require activation by a cocatalyst of the Lewis acid type (e.g. A1C13, GaBr3, TiCU) [66,67], Noble metal chlorides may be used in alcoholic solvents or in water containing emulsifiers [68]. 

Pertinent results for solid state ion exchange of zeolites Rho, ZK-5 and SAPO-42 with noble metal chlorides. 

Solid state ion exchange is a versatile tool for the fast and easy preparation of metal containing small pore (i. e., 8-membered ring) zeolites. Therefore it offers a valuable alternative to the crystallization inclusion method with its limited applicability. The introduction of noble metals into small pore zeolites via solid state ion exchange results in highly shape selective catalysts over which the hydrogenation of the linear alkene out of an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l) is strongly preferred. This indicates that the major part of the metal is located in the intracrystalline voids of the zeolites. Preliminary fUrther experiments in our laboratory surest that the new method is not restricted to noble metal chlorides, but also works with other salts, e. g., oxides and nitrates. 

ZSM-5(Si02/Al203=22.1,TOSOH)-supported noble metal catalysts were prepared by the impregnation method using aqueous noble metal chloride solutions. The metal loading was 5wt%. Catalysts were calcined at 500 C for 4 hr in air and reduced at 450"C for 1 hr prior to use. 

Thus, the electrochemical mechanism of adsorption of noble metal chloride complexes combines a large set of different surface processes and establishes a relationship between them the processes involving components of the gas medium are also included. Analysis of the mechanism allows the following conclusions, which are essentially different from the commonly accepted ideas ... 

Catalysts were prepared by impregnating the noble metal chloride onto either an alumina washcoat or a proprietary washcoat containing alumina, ceria and other base metals. The catalyst was supported on a monolithic cordierite substrate with 64 square cells/cm. Cylindrical cores used for laboratory evaluations were 2.5 cm in diameter and, unless otherwise noted, 5 cm in length. The length of each core was composed of smaller segments taken from various locations down the monolith bed in order to minimize sampling biases. 

The first step is the reductive carbonylation of nitrobenzene to N-phenyl carbamate. This is shown in Eq. (35). The reactor operating conditions are 170 C (340°F) and 95 bars (14(X) psig). Catalyst can be either selenium or a noble metal hallide with a chloride promoter. The catalysts for the reductive carbonylation route, however, are difficult to handle. The selenium catalyst is highly toxic and the noble metal-chloride combination is extremely corrosive. 

The relationship between the lattice energy and the reactivity for SSIE of metal compounds in mixtures with zeolites was generally confirmed by the work of Weitkamp and co-workers (cf. [44,45] and Sect. 5.3) concerning the systems of noble metal chlorides/hydrogen forms of zeolites. It should be noted, however, that such a relationship was not foimd in SSIE experiments with Mn oxides as compounds of the in-going cation [46]. 

TT-Allylpalladium chloride (36) reacts with the nucleophiles, generating Pd(0). whereas tr-allylnickel chloride (37) and allylmagnesium bromide (38) reacts with electrophiles (carbonyl), generating Ni(II) and Mg(II). Therefore, it is understandable that the Grignard reaction cannot be carried out with a catalytic amount of Mg, whereas the catalytic reaction is possible with the regeneration of an active Pd(0) catalyst, Pd is a noble metal and Pd(0) is more stable than Pd(II). The carbon-metal bonds of some transition metals such as Ni and Co react with nucleophiles and their reactions can be carried out catalytic ally, but not always. In this respect, Pd is very unique. 

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

Oxygen and nitrogen also are deterrnined by conductivity or chromatographic techniques following a hot vacuum extraction or inert-gas fusion of hafnium with a noble metal (25,26). Nitrogen also may be deterrnined by the Kjeldahl technique (19). Phosphoms is determined by phosphine evolution and flame-emission detection. Chloride is determined indirecdy by atomic absorption or x-ray spectroscopy, or at higher levels by a selective-ion electrode. Fluoride can be determined similarly (27,28). Uranium and U-235 have been determined by inductively coupled plasma mass spectroscopy (29). 

Titanium is susceptible to pitting and crevice corrosion in aqueous chloride environments. The area of susceptibiUty for several alloys is shown in Figure 7 as a function of temperature and pH. The susceptibiUty depends on pH. The susceptibiUty temperature increases paraboHcaHy from 65°C as pH is increased from 2ero. After the incorporation of noble-metal additions such as in ASTM Grades 7 or 12, crevice corrosion attack is not observed above pH 2 until ca 270°C. Noble alloying elements shift the equiUbrium potential into the passive region where a protective film is formed and maintained. 

Catalysis is done by an acidic solution of the stabilized reaction product of stannous chloride and palladium chloride. Catalyst absorption is typically 1—5 p-g Pd per square centimeter. Other precious metals can be used, but they are not as cost-effective. The exact chemical identity of this catalyst has been a matter of considerable scientific interest (19—21,23). It seems to be a stabilized coUoid, co-deposited on the plastic with excess tin. The industry trends have been to use higher activity catalysts at lower concentrations and higher temperatures. Typical usage is 40—150 ppm of palladium at 60°C maximum, and a 30—60-fold or more excess of stannous chloride. Catalyst variations occasionally used include alkaline and non-noble metal catalysts. 

Usually noble metal NPs highly dispersed on metal oxide supports are prepared by impregnation method. Metal oxide supports are suspended in the aqueous solution of nitrates or chlorides of the corresponding noble metals. After immersion for several hours to one day, water solvent is evaporated and dried overnight to obtain precursor (nitrates or chlorides) crystals fixed on the metal oxide support surfaces. Subsequently, the dried precursors are calcined in air to transform into noble metal oxides on the support surfaces. Finally, noble metal oxides are reduced in a stream containing hydrogen. This method is simple and reproducible in preparing supported noble metal catalysts. 

Fujiwara, M., Matsushita, T., Kobayashi, T., Yamashoji, Y., and Tanaka, M., Preparation of an anion-exchange resin with quaternary phosphonium chloride and its adsorption behavior for noble metal ions, Anal. Chim. Acta, 274, 293, 1993. 

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

These elements are noble metals and, as such, can be dissolved only with great difficulty. The usual leaching agent is hydrochloric acid, with the addition of chlorine to increase the solution oxidation potential. This strong chloride medium results in the almost exclusive formation of aqueous chloroanions, with, under certain circumstances, the presence of some neutral species. Very seldom are cationic species formed in a chloride medium. However, these elements do possess a range of easily accessible oxidation states and, with the possibility of a number of different anionic complexes that are dependent on the total chloride concentration, this provides a very complicated chemistry. A summary of the most important chloro complexes found in these leach solutions is given in Table 11.6, from which the mixed aquochloro and polynuclear species have been omitted. The latter are found especially with the heavier elements. 

Divalent sulfur is a poison for most noble metal catalysts so that catalytic hydrogenation of sulfur-containing compounds poses serious problems (p. 10). However, allyl phenyl sulfide was hydrogenated over tris trisphenyl-phosphine)rhodium chloride in benzene to give 93% yield of phenyl propyl sulfide [674. ... 

---