Post-synthetic HNO3 treatment of ZSM-5 zeolite
synthesized
in the absence of organic structure-directing agent removes framework
Al selectively from the external surface, producing a unique ZSM-5
zeolite catalyst that has very few acid sites on its external surfaces.
The resulting external acid sites can be readily deactivated at the
early stage of the reaction, giving a potentially long-life catalyst
as a result of a high durability to coke formation during the cracking
of hexane or other paraffin molecules.
The effects of hydrogen in the catalytic reforming of n-hexane, which consists of successive isomerization, cyclization, hydrogenolysis, and dehydrogenation, were examined using a palladium membrane reactor through which the hydrogen could be selectively removed from the reacting mixture at temperatures of 250-350 °C and atmospheric pressure. When no hydrogen was added to the feed, significant decreases with time on stream in both the conversion and the activity of catalyst were observed once the flow of sweep gas was started to remove the hydrogen produced in the reforming reaction. This shift in the unexpected direction was found to occur when the hydrogen required to initiate the isomerization step, i.e., the so-called spillover hydrogen, was lacking. When hydrogen was premixed into the feed, stable conversions were obtained, and then removal of the excess hydrogen resulted in an improvement in the conversion of n-hexane.
Diazotization and the Sandmeyer reactions of representative arylamines proceed smoothly in polyethylene glycol-CHzClz and have been found to be effective for the preparation of aryl halides and cyanides.Chemistry in cyclic polyethers (crown ethers) has attracted widespread interest because of the rather high selectivity of many reactions of activated anion species. The properties of polyethylene glycol (PEG) make it an excellent substitute for crown ethers in many reactions,lJ and its use as a co-solvent has been reported. We have now found that diazotization of arylamines and Sandmeyer substitution reactions of the resulting diazonium compounds take place with NaN02-HCl in PEG-CH2C1&4 and with Cu2X2, Cu-MX, or K2[ Cu( CN)4.NH3] in PEG-CH2C12 systems, respectively, providing the first example of the cyano substitution of diazonium salts using the isolated solid K2[Cu(CN)4.NH3] complex (Scheme 1).Ar-NH2 & Ar-Nl Y-5 Ar-X + other products (1) (2) (3) a; Ar = Ph b; Ar = p-PhCOC,H, c; Ar = or-naphthyl d; Ar = p-CIC,H, e; Ar = p-MeOC,H, f; Ar = o-MeOC,H, g; Ar = m-MeOC,H, h; Ar = p-PhGCC6H4 X = C1, Br, I, or CN Y = C1, Br, or I Scheme 1. Reagents: i, NaN0,-HY in PEG-CH,C& at 0 "C; ii, MX in PEG-CH2Cl2 at 0 "C to room temperature.
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