posted on 2023-01-09, 20:15authored byMustapha Yusuf, Gary Leeke, Joseph Wood
The realization of biofuels and chemicals requires the
development
of highly active and selective catalysts, which are resistant to deactivation.
A conventional ZSM-5 (SiO2/Al2O3 =
30) was modified with 0.2 M NaOH to generate a mesoporous zeolite
support. The parent zeolite, mic-ZSM-5, the modified zeolite, hie-ZSM-5,
and a mesoporous silica support, SiO2, were impregnated
with 5% nickel and characterized using X-ray powder diffraction (XRD),
Brunauer–Emmett–Teller (BET) analysis of nitrogen sorption,
scanning electron microscopy with energy dispersive X-ray (SEM-EDX),
transmission electron microscopy (TEM), hydrogen temperature-programmed
reduction (H2-TPR), ammonium hydrogen temperature-programmed
desorption (NH3-TPD), and thermogravimetric analysis (TGA).
The influences of the support properties and solvent during the hydrodeoxygenation
of anisole were investigated by measuring concentration profiles and
rates in a high-pressure batch reactor. NaOH treatment significantly
improved the pore structure, acidity of the support, and metal dispersion
as well as the interaction of nonframework Ni species with zeolite
and, hence, the catalytic activity and selectivity. The highest anisole
conversion of 100% was obtained in 120 min over the hie-Ni/ZSM-5 catalyst
with cyclohexane selectivity of 88.1%. In addition, the Ni/SiO2 catalyst was 84.5% selective to toluene at 48.9% anisole
conversion in 120 min; as such, it was proposed that the transformation
of anisole proceeds via either a direct deoxygenation–hydrogenation
or isomerization–direct deoxygenation pathway. However, no
substantial differences in anisole conversion or product selectivity
were observed when decalin and n-decane were compared
as solvents. A catalyst reusability test showed hie-Ni/ZSM-5 as the
most stable of the three catalysts in terms of anisole transformation,
even though the catalyst recorded the biggest weight loss of 9.2%
suggesting high resistance to carbon deactivation. Therefore, with
this very good catalytic activity, good selectivity to liquid product,
and stability, the mesoporous Ni/ZSM-5 catalyst is a potential candidate
for economically beneficial future industrial applications.