New Catalysts from Spent Catalysts - Spent Hydroprocessing Catalysts - page 246

9.2 Catalysts for Non-Petroleum Applications

The utilization of metal-fouled spent catalysts discarded from heavy oil upgrading processes in
the preparation of active catalysts for reduction of nitrogen oxides has been reported in some
patents [543-545] . The spent catalysts used in these studies contained large amounts of V
together with Mo, Ni, and Co on the alumina support. Besides the above components, coke
and sulfur were also present in the spent catalyst. According to a process developed by Ku
et al. [543] , the spent catalyst was first heated in air at a temperature of around 500 ◦ Cto
remove the coke and sulfur. The resulting coke free materials that contained 11.3% V, 3.4%
Ni, 2.7% Mo, 31.7% Al, 0.8% Co, 0.5% Fe was pulverized into a powder with a size of
200 mesh. The spent catalyst powder was mixed with water and acid or alkali to form slurry
having a viscosity of 40 to 400 cps and a pH of between 3 and 6. The spent catalyst slurry was
deposited in a ceramic comb and then calcined. The catalyst was capable of selectively
reducing nitrogen oxides in the exhaust gas with high efficiency. In another related patent,
Choi et al. [545] used a tungsten impregnated support (e.g. TiO 2 ,

-Al 2 O 3 ) instead of ceramic
honey comb for depositing the spent catalyst metals (e.g. V, Mo, Ni). The catalyst prepared by
this process was very advantageous in terms of selectivity for reduction of nitrogen oxides as
well as better poisoning resistance to sulfur oxides. Further improvements in the performance
of such catalysts for selective reduction of nitrogen oxides from exhaust gases was achieved by
these authors by using spent catalysts that contained low concentrations of V and high
concentrations of Mo [546] . The catalyst preparation procedure comprised the
following steps:

(1) Pretreating a spent catalyst discharged from a hydro-desulfurization process of an oil
refinery, which comprises 4 wt.% or less of vanadium, 4 wt.% or less of nickel, 5 wt.% or
more of molybdenum and 1 wt.% or less of sulfur on an alumina support by thermally
treating said spent catalyst followed by washing with water.

(2) Providing a titania impregnated with 3 to 10 wt.% of tungsten on the basis of titania weight.

(3) Pulverizing the pretreated spent catalyst, followed by homogeneously mixing the
pulverized spent catalyst with the tungsten-impregnated titania under the addition of water
and acid.

(4) Dehydrating the mixture to remove excess moisture and active metal components therein.
(5) Drying the dehydrated mixture at 100 to 200 ◦ C for 9 h or longer, followed by grinding the
dried mixture.

(6) Forming a catalyst body by extruding the grinded mixture or coating the grinded mixture
to a structure, followed by drying under a constant temperature and humidity condition
and then calcining the dried structure.