SYNTHESIS AND CHARACTERIZATION OF ZEOLITE BETA SUPPORTED Fe AND Ni CATALYSTS FOR STEAM GASIFICATION OF PALM KERNEL SHELL FOR HYDROGEN PRODUCTION

Production of hydrogen gas (H2) from biomass gasification usually comes with
several problems such as the existence of unacceptable level of tars and also
ineffectiveness of the catalysts’ performance due to coke deposition. In order to
eliminate most of the inconvenience encountered, new types of catalysts have been
developed. In this study, monometallic Fe and Ni supported on zeolite beta (BEA)
have been prepared by incipient wetness impregnation method. Fe and Ni based
bimetallic catalysts supported on BEA were also prepared using two different
approach; sequential impregnation and co-impregnation method. The BEA support
was impregnated with the solution containing the required amount of metal salts for
4 hours, dried at 120 oC for 16 hours and later calcined at temperatures between 500-
700 ºC for 16 hours. These catalysts were structurally characterized using BET,
XRD, FESEM-EDX and TPR. A screening process was performed at temperatures
between 600 – 900 oC in a fixed-bed quartz micro-reactor in the absence of a catalyst
to determine the optimum temperature for the steam gasification of palm kernel shell
(PKS) to H2. The gases produced were analyzed using two on-line gas
chromatographs; to analyze sulphur compound in the product gases and to determine
the composition of H2, CH4, CO and CO2. The catalysts were then tested for their
ability to produce H2 in the steam gasification of PKS in a fixed-bed quartz microreactor
with an on-line gas chromatograph at 700 ºC. BET analysis shows that the
isotherms plots of the prepared catalysts are type IV which is mesoporous materials.
Moreover, the Fe-Ni/BEA catalysts possess lower surface area, higher pore volume
and larger pore diameter as compared to other prepared catalysts. Calcination
temperature is found to contribute to the crystallization of the prepared catalysts
where high crystallization of Fe and Ni was observed in Fe-Ni/BEA (700) catalyst
with the formation of NiO and NiFe2O4 phase. The TPR profiles of the bimetallic
catalysts show the combination of nickel and iron phases’ reduction which attributed
to weak interaction with support (NiO and Fe2O3 phase) and strong interaction with
the support (NiAl2O4 and FeAl2O4). From the screening process, the optimum
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temperature for steam gasification of PKS is 700 ºC. This is because maximum of H2
evolvement was achieved at 700 ºC without existence of H2S. The differences in the
physicochemical properties of the catalysts affect the catalytic performance whereby
it exhibit the PKS to undergo either steam reforming for higher in H2 evolvement or
facilitates the oxidation of CO to produce more CO2. In terms of monometallic, both
Ni/BEA (500) and Fe/BEA (600) catalysts show the highest concentration of H2
evolved where Ni/BEA (500) catalyst has higher reducibility and surface area while
Fe/BEA (600) has larger pore diameter. For bimetallic catalysts, the highest
concentration of H2 evolvement in the steam gasification of PKS achieved in the
presence of FeNi/BEA (700) and NiFe/BEA (500). At a suitable calcination
temperature, FeNi/BEA able to enhances the water gas shift reaction while
NiFe/BEA facilitates the steam methane reforming. However, in co-impregnation
catalyst, both Fe and Ni promote the active site of the catalyst to increase the
crystallization of NiFe2O4 and exhibit the steam methane reforming as well as water
gas shift reaction. Fe-Ni/BEA (700) shows the highest composition of H2 gas evolved
with 76.32 vol% H2, 18.72 vol% CO2, 4.96 vol% CO and the absence of CH4. The
outlet gas composition also shows that the steam gasification of PKS in the presence
of Fe-Ni/BEA (700) has a potential to replace the commercial methane reforming for
H2 production. Therefore, it can be concluded that various parameters in catalyst
preparation resulted in deviation in the catalyst properties and interaction between
the active metals with support as well as the catalytic activity.