Chemistry Reference
In-Depth Information
Ghampson et al.
196
studied other types of supports like alumina and
SBA-15 silica with MoN as active phase. HDO of guaiacol was studied in a
batch reactor at 300 1C and 50 bars of H
2
. Both the activity and selectivity
of these two systems were different. Alumina performed with highest
activity via catechol, while SBA-15 formed phenol directly by demethoxy-
lation with very little catechol formation. Nitridation by ammonolysis was
found to be slightly better than with H
2
/N
2
. Different phases of nitride
were formed, depending upon procedure and supports. Ammonolysis
gave g-Mo
2
N on SBA-15, while H
2
/N
2
gave b-Mo
2
N
0.78
. The lack of
catechol formation with silica is proposed to be important for min-
imizing coke formation. Silica also contains widely different types of pore
systems, which opens up to adapting HDO for diverse biomass derived
feed streams.
Unsupported Mo
2
N has also been studied
194
for guaiacol HDO in a
batch reactor set-up (300 1C, 50 bars H
2
). The materials were prepared by
thermal decomposition of ammonium heptamolybdate to form MoO
3
and nitrided in either NH
3
or H
2
/N
2
. The highest activity and highest
phenol/catechol product ratio was obtained by ammonolysis, and was
attributed to the g-Mo
2
N phase and the highest N/Mo ratio. Promotion by
Co was attempted but a single phase cobalt molybdenum nitride was not
formed.
Phosphides. Phosphide materials that earlier were considered of
interest for other applications are now evaluated as interesting for HDO.
In the late 50's, Sweeny et al.
55
published a paper on the use of Ni
phosphides for the vapour phase reduction of nitrobenzene with hydro-
gen to aniline and water. Later on, during the 70's, Nozaki's group em-
ployed nickel phosphide supported on alumina for studying the activity
for the partial hydrogenation of 1,3-butadiene.
58,197,198
Furthermore, re-
ports from the 90s showed a promising activity of transition metal
phosphides for HDN and HDS.
46,47
Fairly recently, the same materials
have been proved to be promising for HDO, as documented by studies
with model compounds.
50
Figure 9 shows a comparison of turnover
frequencies for guaiacol conversion on transition metal phosphides.
Fig. 9 Turn-over frequency of guaiacol on transition metal phosphides. Reproduced with
permission from ref. 50.
