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Fig. 8 The intrinsic activity for maleic anhydride (mol h
1
m
2
). 1.5% butane/air, 400
1
C. For
VPA/VPO/VPD catalysts, GHSV
=
1200 h
1
; for all other catalysts, GHSV
=
2400 h
1
.
(LP)
=
liquid CO
2
preparation, (EP)
=
evaporation preparation, (SCP
1
)
=
SC-CO
2
preparation.
Reproduced from Journal of Catalysis, (2002), 208, page 200 with permission of Elsevier.
required to establish steady state performance, showing that an
amorphous vanadium phosphate material is active and selective to
maleic anhydride, adding weight to the amorphous overlayer hypothesis
for catalysts prepared by standard routes.
As presented in Fig. 8 the intrinsic activity relative to the surface area
of the catalysts was higher for the materials prepared using CO
2
anti-
solvent precipitation. The GHSV of the novel materials was twice that of
the standard materials, which further emphasizes the improvement in
activity of the SAS synthesised catalysts. Although the intrinsic activity of
the VPO
SCP1
was higher than that achieved by the standard preparation
routes (VPA, VPO, VPD), the surface areas were substantially lower. This
resulted in a lower mass normalised activity for the VPO
SCP1
than those
observed for standard materials. However, this does not detract from the
significance of the work, as it is one of the first detailed studies on the
application of catalyst preparation using SAS precipitation. This study
also highlights the potential and feasibility for the synthesis of more
complex catalysts using the SAS process, and that it can be extended to
other catalyst systems like phosphates.
The preparation of copper/manganese oxide (Hopcalite), as an ambi-
ent CO oxidation catalyst using SAS precipitation has been investigated in
several studies.
62-64
Initial studies investigated the SAS precipitation of
copper(II) acetate monohydrate and manganese(II) acetate tetrahydrate
(Mn : Cu ratio of 2 : 1) from a DMSO solution. The resulting precipitate
comprised of an intimate mixture of the amorphous metal acetates.
Conditions used were typical of SAS precipitation with operating pressure
of 110 bar and 40 1C temperature. The surface area of this SAS precipi-
tated material was substantially higher, at W300 m
2
g
1
, than that of the
two starting metal acetate salts. Calcination of the SAS material at 300 1C
resulted in the formation of a crystalline CuMn
2
O
4
phase with surface
area of 20 m
2
g
1
. It is interesting to note that preparation of crystalline
