Recent Developments in Gold Nanomaterial Catalysts for Oxidation Reaction through Green and Sustainable Routes - Advanced Materials for Agriculture, Food and Environmental Safety - page 206

Is omerizati on

CH 3 CH 2 C= O
H

CH 3 CH 2 C= O

C O 2

O H

H O CH 2 CH 2 CH 2 O H

CH 3 CCH 3
O

H O CH 2 CHCH 3

C O CH 2 CCH 3

CH 3 CH-CH 2
O

O

O

H 3 CC= O

O

H 3 CHC CH 2

CHCH 3

O H

H 2 C

O

H 3 CCHCH 2

CH 3 C= O

CH 3 C= O

O

Cracking

H 3 CC= O

H O H

Figure 8.7 Probable side reactions occurring on Au/Ti-MCM-48 catalyst during direct
propylene epoxidation reaction. (Obtained from presentation of M. Haruta, Tokyo
Metropolitan University).

(Figure 8.7). h is might be due to the presence of acidic sites in the catalyst
which form oligomerized byproducts, thereby covering the catalyst sur-
face, leading to deactivation. Sinha et al. [80] speculated that an increase
in hydrophobicity in the catalyst surface might control the adsorption of
PO on the catalyst surface, improving the PO yield steady state in time
over stream (Figure 8.8). Even though they could improve the catalyst per-
formance with respect to propylene conversion, PO selectivity and hydro-
gen ei ciency, they failed to control the deactivation. Later Chowdhury
et al. [72] made an attempt to use a small amount of trimethylamine as a
gaseous promoter on the promoted mesoporous titanosilicate catalyst and
were successful in keeping the catalyst activity steady for up to a 10 hour
run. It is found that there is an optimum concentration of trimethylamine
in the range of 10-15 ppm present during pretreatment and cofeed to i nd
the best ef ect on the catalyst performance (Figure 8.9).
Also, they observed that regenerated catalyst gave almost equal activity
to that of the fresh catalyst, which was quite interesting for recycling cat-
alyst for successive runs (Figure 8.10). Attempts to improve the PO yield
by changing the reaction parameters like pretreatment temperature and
condition, reaction temperature, space velocity and feed composition are
well documented in the literature. h ey found that catalyst pretreatment
at 250 ° C in the presence of molecular H 2 and O 2 , reaction temperature at

150 C, space velocity of 4000 h -1 and Ar:Py:H 2 :O 2 (70:10:10:10) is ef ective.

Based on the experimental evidence described above, TS-1, which is
a naturally hydrophobic microporous material, and supported nanogold
catalysts are supposed to give the best results. Recent results from the

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