An investigation into coking on catalyst support materials supported metal catalysts

摘要

The deposition of coke on oxidation catalysts leads touddeactivation. For oxide supports this phenomena of coking has previously been identified with acidic sites. Measurement of coke formation on silica gel, a-, r|- and y-Al2 0 3 showed that the greatest amount of coke was formed on y-A12 0 3 followed by r(-Al2 0 3 with no detectable coking occurring on either a-Al2 0 3 or silica gel. Titration results showed y-Al2 0 3 to contain the highest concentration of acidic and Bronsted basic sites per gram followed by ri-Al2 0 3, a-Al2 0 3 and silica gel.ududThe acidity of y-Al20 3 was altered by treatment with HC1, NH3 and NaOH. HC1 treatment gave a reduction in coke deposition while NaOH treatment increased coking and NH3 treatment had no effect on the level of coking.ududThe effect of doping y-Al2 0 3 and 0.5%Pt/y-Al20 3 with Sn, Ce and Zr on the amount of coke formed was investigated. It was found that the level and method of impregnation affected the amount of coke formed on each catalyst. Individual addition of Sn, Ce, or Zr to y-Al2 0 3 brought about a large reduction in the level of coking relative to y-Al20 3 with the greatest reduction being seen for addition of Zr. Doping Pt/y-Al2 0 3 with Ce, Sn or Zr resulted in the lowest level of coking occurring on Pt-Sn/y-Al2 0 3. No correlation between acidic and Bronsted basic sites was observed for the metal impregnated catalysts suggesting that these metals exert a much greater influence on coking than do acidic or Bronsted basic sites.ududThe effect of Sn, Ce or Zr addition on activity of Pt/y-Al2 0 3 for oxidation of isobutane was investigated. Addition of Sn or Zr reduced activity while 0.3% and 3.0% Ce resulted in greater activity than that observed for Pt/y-Al2 0 3.