Available online at BCREC Website: http://bcrec.
Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 160-166 Research Article Hydrogen Production via Glycerol Dry Reforming over La-Ni/Al2O3 Catalyst Kah Weng Siew1.
Hua Chyn Lee1.
Jolius Gimbun1,2.
Chin Kui Cheng1,2,* Faculty of Chemical & Natural Resources Engineering.
Universiti Malaysia Pahang.
Lebuhraya Tun Razak, 26300 Gambang.
Kuantan Pahang.
Malaysia Center of Excellence for Advanced Research in Fluid Flow.
Universiti Malaysia Pahang.
Lebuhraya Tun Razak, 26300 Gambang.
Kuantan Pahang.
Malaysia Received: 12nd May 2013.
Revised: 7th October 2013.
Accepted: 16th October 2013 Abstract Glycerol .
bio-waste generated from biodiesel productio.
has been touted as a promising bio-syngas precursor via reforming route.
Previous studies have indicated that carbon deposition is the major performance-limiting factor for nickel (N.
catalyst during glycerol steam reforming.
In the current paper, dry (CO.
-reforming of glycerol, a new reforming route was carried out over alumina (Al2O.
-supported nonpromoted and lanthanum-promoted Ni catalysts.
Both sets of catalysts were synthesized via wet coimpregnation procedure.
The physicochemical characterization of the catalyst showed that the promoted catalyst possessed smaller metal crystallite size, hence higher metal dispersion compared to the virgin Ni/Al2O3 catalyst.
This was also corroborated by the surface images captured by the FESEM analysis.
BET surface area measurement gave 92.
05mA/g for non-promoted Ni catalyst whilst promoted catalysts showed an average of 1 to 6% improvement depending on the La loading.
Reaction studies at 873 K showed that glycerol dry reforming successfully produced H 2 with glycerol conversion and H2 yield that peaked at 9.
7% and 25% respectively over 2wt% La content.
The optimum catalytic performance by 2%LaNi/Al2O3 can be attributed to the larger BET surface area and smaller crystallite size that ensured accessibility of active catalytic area.
A 2013 BCREC UNDIP.
All rights reserved Keywords: biofuel.
dry reforming.
How to Cite: Siew.
Lee.
Gimbun.
Cheng.
Hydrogen Production via Glycerol Dry Reforming over La-Ni/Al2O3 Catalyst.
Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
: 160166.
oi:10.
9767/bcrec.
Permalink/DOI: http://dx.
org/10.
9767/bcrec.
Introduction As the world still grappled with energy crunch scenario, there is no indication of slowing demand for fossil fuels.
hence a concerted search for alternatives to petroleum based fuels is clearly needed.
* Corresponding Author.
E-mail: chinkui@ump.
my (C.
Chen.
Tel: 60-9-5492896.
Fax: 60-9-5492889 Chief among the identified alternative fuels, hydrogen (H.
gas is touted as the most promising option due to its clean emission and high efficiency.
Indeed, it has been professed that Malaysia has bright potential in large-scale H2 production particularly from biomass such as glycerol.
The utilization of waste glycerol .
rom local biodiesel productio.
potentially lowers the production cost of biodiesel plants .
Significantly.
B5 palm oilbiodiesel blend has been used in Malaysia .
With bcrec_4874_2013 Copyright A 2013.
BCREC.
ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 161 large land bank for oil palm cultivation, it provides sustainable availability of raw material for biodiesel production and hence plethora glycerol byproduct.
Recently, concerted scientific efforts have been undertaken to produce H2 gas via steam reforming route.
This process requires H2O .
whilst releasing CO2 as a byproduct .
The primary drawbacks hence are strongly related to the energy-intensive steam production and the release of greenhouse gas CO2.
Therefore, the current work employs dry reforming process to replace steam reforming.
H2 production via dry reforming technique is reported as a greener process as it consumes CO2 while releasing H2O as the by-product .
The availability of bountiful glycerol as the raw material coupled by the green H2 production .
ia dry reformin.
is believed to offer a better pathway for glycerol dry reforming reaction.
The overall glycerol dry reforming can be represented as in Eq.
C3H8O3.
CO2.
Ie3H2.
4CO.
H2O.
Materials and Methods A series of 0 to 5 wt% La promoted 20 wt% Ni/Al2O3 catalysts were synthesized via co-wet impregnation method.
Nitrate solutions of predetermined metal loadings of respective precursors were mixed with accurately weighed solid alumina.
The obtained slurry was then stirred for 3 h and subsequently oven-dried for 24 h.
Finally, the dried solid was calcined at 1023 K for 6 h followed by sieving to 90-140 Am.
Catalyst characterization was performed to obtain BET surface area.
XRD scanning.
FESEM imaging and EDX analysis.
For glycerol dry reforming experimental work, pristine glycerine grade was directly injected into a 10-mm diameter fixed-bed reactor system at 873 K via a HPLC pump (LabAlliance Series .
while CO2 was individually flowed to the reactor as a reforming For all the runs, the ratios of reactants were controlled at unity.
N2 was applied as a carrier gas.
Prior to the experiment.
H2 at 50 ml/min was metered into the reactor for catalyst activation.
The amount of hydrogen gas produced was determined using Agilent gas chromatography (GC) with TCD capillary columns.
HP-MOLSIV (Model No.
Agilent 0 m y 530 m y 50.
and HPPlot/Q column (Model No.
Agilent 19095-Q04.
m y 530 m y 40.
under an oven temperature of 393K.
Helium gas was used as a carrier gas.
For pure calcined alumina sample, it can be observed that the XRD pattern only shows the existence of -alumina with shorter and broader peaks.
This form of alumina support has bigger surface area as proven by the subsequent BET surface area measurements.
In addition, it can be observed that the diffraction peak of alumina after impregnation with nickel .
esulting in Ni/Al2O3 sampl.
has shifted to the lower 2AAvaluesaihis can be attributed to the diffusion of NiO into the support to form NiAl2O4 phase as confirmed by Zangouei et al.
For all the lanthanum (L.
-promoted catalysts, it can be seen that similar peaks representing NiAl2O4 phase at 2 of 37.
0A, 44.
9A and 65.
5A were obtained indicating near-similarity of crystalline structure amongst the samples.
Interestingly.
Ladopant species was undetectable from the XRD Most likely.
La3 which is a considerably large ion and hence difficult to diffuse into the supportAos vacant sites.
Consequently, it exists as La 2O3 with high metal dispersion .
within the solid matrix.
The finely-dispersed La2O3 practically ensures lesser carbon deposition, improves catalyst sintering and an increase in surface area .
In addition, the intensities of peaks .
ncluding NiO) decreased with La content.
Moreover, at 4 wt% and 5 wt%-La respectively.
NiO peak was undetectable .
Figure The absence of NiO peak indicated that the NiO species was well-dispersed and cannot be detected after a particular level of promoter addition .
Furthermore, it seems that the major diffraction peaks had broadened with amounts of La-promoter incorporated indicating formation of smaller crystallites.
Results and Discussion X-Ray Diffraction Characterization Figure 1 shows the crystallinity structure of calcined catalyst samples via exhibitions of sharp/ shoulder peaks at different diffraction angles .
A).
Figure 1: XRD pattern of prepared calcined catalysts:
-Al2O3.
NiAl2O4.
Copyright A 2013.
BCREC.
ISSN 1978-2993 NiO Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 162 2 FESEM-EDX Characterization 1 FESEM Characterization Figure 2 shows the surface morphology of the The particle size and porosity were different for calcined alumina.
Ni/Al2O3 and LaNi/Al2O3 catalysts respectively.
For calcined Al2O3 support .
Figure 2.
), it can be observed that the surface was smoother with few crystallites formed and larger pores.
This can be supported by the BET surface measurements in Section 3.
3 that show surface area of pure calcined alumina as the largest compared to other samples.
Post Niimpregnation, the surface of the Ni/Al2O3 catalyst .
Figure 2.
) becomes rougher.
The bulkier and rougher structures were an attribute of both NiO and NiAl2O4 species.
The presence of these two species was confirmed by the preceding XRD patterns in Section 3.
It can also been observed that upon introduction of both Ni and La metals, the pores of the alumina support was blocked by the formation of new crystallite species, resulting in less porous catalysts.
The FESEM image of 2 wt% La-Ni/Al2O3 catalyst .
Figure 2.
) shows that the crystal particles has smaller crystallite diameter compared to the Ni/Al2O3 due to the AospacerAo role played by the La2O3 species that avoids the crystallites from aggregating and forming large particles particles as indicated in Figures 2.
Consequently, the 2 wt% La-Ni/Al2O3 possesses a higher surface area than the Ni/Al2O3.
Similarly, the FESEM image of 3 wt% La-Ni/Al2O3 .
Figure 2.
) shows even finer crystallite structures or particles compared to 2 wt% La consistent with XRD patterns.
Moreover, it can also be observed that the pores on the surface of 3 wt% La-Ni/Al2O3 are nearly unnoticeable as most of the pores had been covered by the smaller crystallite.
Hence, an addition of higher promoter amount may not necessarily increase the activity as it may also cover most of the active sites on the catalyst .
Al2O3 .
2% La-Ni/Al2O3 .
Ni/Al2O3 .
3% La-Ni/Al2O3 Figure 2.
Morphology structure of the calcined .
Al2O3, .
Ni-Al2O3, .
2 wt% La-Ni/Al2O3 and .
3 wt% La-Ni/Al2O3 catalysts Copyright A 2013.
BCREC.
ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 163 2 EDX Characterization EDX measurements were taken to determine the actual metal loading on the synthesized catalysts.
Tables 1 to 4 show the actual metal loading detected by EDX analysis for alumina support, unpromoted Ni/Al2O3 catalyst and La-promoted catalyst respectively.
Figure 3 illustrates the peaks representing types of element present in unpromoted and several promoted catalysts as function of surface energy .
eV).
EDX for alumina shows the existence of peaks for Al .
5 keV).
O .
keV) and C elements only while EDX pattern for Ni/Al2O3 records the peaks representing Ni .
ecorded at 0.
9 keV).
Al.
O and C.
The EDX pattern for all La-promoted Ni/Al2O3 catalysts gave peaks for La and Ni elements .
uperimposed at 1.
keV).
Al.
O and C.
In addition, the catalyst with higher La promotion .
wt% La-Ni/Al2O.
as shown in Figure 3.
depicts higher La-element peak compared to the lower La promotion catalyst .
Figure 3.
The existence of C in the result was due to the carbon tape employed to stick the samples onto the sample holder.
Al2O3 .
3% La-Ni/Al2O3 .
2% La-Ni/Al2O3 .
3% La-Ni/Al2O3 Figure 3.
Compositions of elements in the unpromoted and promoted catalysts Table 2.
EDX analysis of Ni/Al2O3 Table 1.
EDX analysis of alumina
Weight% Compd% Formula
Element
Weight% Compd% Formula
CO2
Al2O3
CO2
Al2O3 NiO Element Table 3.
EDX analysis of 2 wt% La-Ni/Al2O3 Table 4.
EDX analysis of 3 wt% La-Ni/Al2O3 Element Weight% Compd% Formula Element Weight% CO2 Al2O3 NiO La2O3 Copyright A 2013.
BCREC.
ISSN 1978-2993
Compd% Formula
CO2
Al2O3 NiO La2O3 Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 164 3 BET Characterization The liquid N2-isotherms in Figure 4 show similar hysteresis indicative of mesoporous structure for all the synthesized catalysts.
Significantly, formation of the type H3 hysteresis loop from the analyses is symptomatic of the aggregation of plate-like material that leads to the formation of slit-like pores .
In addition.
BET results also showed that all the samples exhibited large specific surface area.
It can be seen from Figure 5 that the calcined alumina support has the highest specific surface area .
9 m2/.
among the samples.
The surface area of the Ni/Al2O3 decreased compared to the alumina support because the pores on the alumina support were covered by the loaded nickel species crystallites as aforementioned.
Nevertheless, the Ni/Al2O3 catalyst still possessed high surface area .
0 m2/.
Significantly.
BET surface area of the 1 wt% La-Ni/ Al2O3 and 2 wt% LaNi/Al2O3 has increased compared to unpromoted Ni/Al2O3.
This indicates that incorporation of La has increased the surface area catalyst, consistent with the preceding XRD and FESEM results.
Al2O3 Smaller nickel species crystallite has led to a higher surface area.
Nonetheless, the surface area of catalysts reduced beyond 2 wt% La loading.
Once again, this can be attributed to the more extensive blocking of pores as crystal becomes smaller .
Figure 2.
Consequently, higher promoter loading may not necessarily enhance the specific surface area.
4 Reaction Study Figure 6 shows the result compilation of transient H2 yields during the dry reforming of glycerol reaction over Al2O3 support.
Ni/Al2O3, and Lapromoted Ni/Al2O3 catalysts at 873K for the continuous 120 min.
It exhibits the reaction stability and H2 yield of all reaction runs that rapidly attaining steady-state.
At time of 120 min, it can be observed that 2 wt% La-Ni/Al2O3 gave the highest H2 yield of circa 9.
7% while alumina only produced It also can be seen that 5 wt% La-doped catalyst showed poorer performance compared to 2 wt% and 3 wt% La-promoted catalysts.
As afore- .
2% La-Ni/Al2O3 .
Ni/Al2O3 .
3% La-Ni/Al2O3 Figure 4.
BET isotherm of some catalysts samples Copyright A 2013.
BCREC.
ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 165 mentioned, this may be explained by the excessive doping of La that resulted in the encapsulation of the available active sites.
Figure 7 shows the H2 production as a function of La%-promotion whilst Figure 8 shows the glycerol conversion trend.
Interestingly, both H 2 yield and glycerol conversion exhibited a volcano-shaped curve with respect to the La-metal loading.
The H2 yield and glycerol conversion decreased in the order of 2 wt% La-Ni/Al2O3 > 3 wt% La-Ni/Al2O3 > 4 wt% La-Ni/Al2O3 > 1 wt% La-Ni/Al2O3 > Ni/Al2O3 > 5 wt% La-Ni/Al2O3 > Al2O3.
In particular, both H2 yield and glycerol conversion for 2 wt% La-Ni/Al2O3 catalyst gave the highest values at time of 120 min reaction, recorded 9.
67% and 24.
47%, respectively.
Significantly, this can be attributed to the high specific surface area, active sites distribution, highly dispersed metallic nickel species on the catalyst surface, and well-developed mesoporosity in facilitating internal mass transfer of reactant and product in the dry reforming reaction .
Against the backdrop of XRD results, it can be concluded that the H2 production and glycerol conversion has increased when the Ni crystallite size was decreased via La-metal incorporation.
However, the addition of La amount exceeding 2 wt% has led to the reduction in both H2 yields and glycerol conversion although Ni crystallite size is reduced.
This is due to La overloading on the catalyst surface.
La overloading causes clogging resulting in most of the active site being covered up, hence decreased the catalytic reactivity.
Significantly, it has been reported before that excess La amount could cover the active sites of a catalyst .
Figure 5.
BET Surface area variation at different La loadings Figure 7.
Hydrogen yield as function of La content Figure 6.
Transient hydrogen yield at 873 K Figure 8.
Glycerol conversion as a function of La Conclusion The effects of La-promoted Ni based catalyst have been examined and subsequently glycerol dry reforming were carried out at reactant ratio of unity and temperature of 873 K.
Physicochemical characterization of the synthesised catalysts re- Copyright A 2013.
BCREC.
ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 8 .
, 2013, 166 vealed that the addition of La-oxide as promoter has contributed to the fine dispersion of active metal sites over the alumina support.
This also explained the larger BET surface area obtained for promoted catalyst compared to the non-promoted Ni/Al2O3 catalyst.
Results from glycerol dry reforming experimental works have suggested that this new H2 producing route is very promising with transient catalytic stability of at least 120 min of reaction and that the best catalytic performance was obtained for reforming over 2 wt% La-Ni/Al2O3 Acknowledgements Authors would like to thank MOHE for the provision of MTUN-CoE research grant with vot.
RDU121216.
Kah Weng Siew is a grateful recipient of the GRS scholarship from the Universiti Malaysia Pahang.
References