Page 200 - Advances in bioenergy (2016)

34
shown in Table 8.3. On the other hand, oxides having basic sites may lead to the formation of
acetaldehyde, through an aldol condensation reaction to higher oxygenates production; as a
result, the formation of dimethyl ketone was favored over ZnO during steam-reforming (SR)
35
conditions at higher space time (h). Fermoso et al. tried to achieve high yield (88%) and
purity of H up to (99.7 vol%) at atmospheric pressure and at 550–600°C with a S/C = 3, in a
2
fixed-bed reactor by applying Ni/Co catalyst derived from hydrotalcite-like material (HT) and
36
dolomite as CO sorbent. They revealed that the concentration of methane is lowest at 575°C,
2
while the CO concentration increases concurrently with increasing temperature from 525 to
600°C. The high coking potential of glycerol and fatty acid methyl esters (C –C ) resulted in
19
17
the increased formation of coke, thus lowering the hydrogen yield. The reaction rates of
methane reforming and WGS reactions are much higher than the steam reforming of crude
glycerol on Co-Ni catalysts. The oxidative steam reforming of bio-oil under controlled O 2

environment can yield better H by utilizing the exothermic heat of reactions.
2
The promoter effect of CeO is related to the ability of (1) acting as an oxygen storage material
2
in oxidation reactions, (2) dispersing active noble metal phases inhibiting their sintering, (3)
promoting WGS, and (4) facilitating the coke gasification. Addition of ZrO to CeO manifolds
2
2
the activity of ceria while increasing the OH mobility at the surface of catalyst with the help of
added oxygen mobility. Several ESR reaction mechanisms have been proposed by different
groups, whereas WGS reaction plays an important role towards the distribution of products. 33

Bio-oil is difficult to reform completely, but steam reforming of the main components in bio-oil
such as acetic acid (12–14% by wt.), ethanol, and glycerol is feasible. Takanabe et al. have
studied the CSR of acetic acid over Pt/ZrO catalyst, and Basagiannis and Verykios, and Xun
2
and Gongxuan investigated the influence of Ni and noble metals with supports (Al O ,
2 3
La O /Al O , MgO/Al O ) on CSR of acetic acid. 37-39 Takanabe et al. and Vagia and
2 3
2 3
2 3
Lemonidou studied the thermal decomposition and its reforming tendency in the absence and
presence of steam for different metals supported by calcium aluminate. 40,41 Coke deposition on
the catalyst surface is a serious problem and the rate of coke formation is higher in case of
nickel catalyst in comparison to noble metal catalyst; besides, noble metal catalysts are very
expensive. The catalyst preparation and selection of support are the two crucial factors for
higher hydrogen yield, low methane and carbon monoxide formation, and low deactivation rate

of the active sites of the catalyst. This review has tried to summarize different catalysts such as
Co-Fe, Co(R), Ni-Al-Ca, Ni-Al, Ni-Co-Al, Ni-Ce-Zr, Co-Al, Co-Ce-Al, Co-La-Al, Ni-Zr, Ni-
Co, Cu-Zn-Ca-Al, Ni-Ca-Al, Mg-Ca, Pt-Zr and Ni-Pd-Ag in membrane reactor at counter
current operation for H generation, as shown in Table 8.4. 40,42-50,60-62 Some metals such as
2
Cu-Zn-Ca-Al, Co-Fe, Co(R), and 5%Ni-Ca-Al have delivered higher %H yield (>70–90%)
2
with >80% acetic acid conversion. These selected catalysts are inexpensive and recovery of
metal for recycling usage is also easy to generate hydrogen from acetic acid. Similarly,
different catalysts such as Ni-Ce, Ni-Mg, Ni-Ti, Ni-Al, Ni-Mg-Al, Ni-Cu-Al, Ni-CuMg, Ni-
Mg, Ni-Ce-Zr-Al, Rh-Ce-Al-Si, Pt-Al-Si, Pd-Cu-Ni-K, and novel metals such as Ir-La, Pt-Si,