548
higher reaction temperatures and tedious hydrogen purification processes due to
high CO contents [291, 301].
Tokarev et al. [302] reported nearly complete conversion (98.3%) of 10% ethanol in water, during APR on Pt/Al 2 O 3 catalyst at 225 °C and 29.3 bar pressure, in
continuous-flow mode and observed hydrogen production of 0.15 mmol/min and
stable activity. Addition of 10% sorbitol or 10% glycerol to aqueous ethanol solution resulted in increase of hydrogen production to 0.71 and 0.30 mmol/min, respectively, along with methane and CO formation. In the case of alumina (prepared by
solution combustion synthesis—SCS)-supported Ni (10% w/w loading) catalyst for
ethanol reforming, Roy et al. [303] observed that surface modification of the catalyst by non-thermal RF plasma treatment resulted in improvement in the ethanol
conversion from 81.2% on unmodified catalyst to 85.9% on modified one at 225 °C,
which displayed no deactivation for 144 h. Hydrogen yield was also higher, at
381 μmol/min for modified catalyst in comparison with 334 μmol/min for unmodified one. Roy et al. [303] attributed the superior performance of plasma-treated catalyst to an increase in Ni metal dispersion, stronger metal-support interaction and
increase in acidity. Detailed studies on the influence of preparation methods for Ni/
Al 2 O 3 [304, 305] and Ru/TiO 2 [306] catalysts on the performance for ethanol
reforming process have also been reported. Nickel supported on Mg-Al hydrotalcites with basic character and higher surface area and pore volume displays
higher ethanol reforming activity compared to Ni/Al 2 O 3 [307]. Though n-butanol
has higher hydrogen content (13.5% w/w) compared to ethanol (13%) and methanol
(12.5%), n-butanol conversions are low, 5.77% on Ni/CeO 2 and 2.77% on Ni/Al 2 O 3
at 488 K [308]. Both noble metal (Pt, Pd) and non-noble metal (Ni) catalysts have
been explored for reforming of sorbitol and xylitol [289]. Higher hydrogen yield
and hydrogen selectivity were observed for xylitol in comparison with sorbitol,
since its longer carbon chain leads to higher alkane formation.
Comparative evaluation of the APR activity of different alcohols has been
reported albeit with some contradictions. While Shabaker et al. [309] reported similar APR rates for methanol and ethylene glycol on Pt/Al 2 O 3 , with higher hydrogen
production rate for methanol, Liu et al. [310] reported higher ethylene glycol
reforming rates with higher hydrogen selectivity compared to methanol, on Pt catalysts on five different supports.
According to Cortright et al. [283], amongst different alcohols, maximum selectivity for hydrogen production was observed with methanol, with lowest CO 2 production, since it has lowest number of carbon atoms (Table 7).
These studies reveal that C-C bond cleavage is not the decisive step in APR process and the reaction mechanism varies with the type and molecular structure of the
substrate alcohol.
R. Vinayagamoorthi et al.
higher reaction temperatures and tedious hydrogen purification processes due to
high CO contents [291, 301].
Tokarev et al. [302] reported nearly complete conversion (98.3%) of 10% ethanol in water, during APR on Pt/Al 2 O 3 catalyst at 225 °C and 29.3 bar pressure, in
continuous-flow mode and observed hydrogen production of 0.15 mmol/min and
stable activity. Addition of 10% sorbitol or 10% glycerol to aqueous ethanol solution resulted in increase of hydrogen production to 0.71 and 0.30 mmol/min, respectively, along with methane and CO formation. In the case of alumina (prepared by
solution combustion synthesis—SCS)-supported Ni (10% w/w loading) catalyst for
ethanol reforming, Roy et al. [303] observed that surface modification of the catalyst by non-thermal RF plasma treatment resulted in improvement in the ethanol
conversion from 81.2% on unmodified catalyst to 85.9% on modified one at 225 °C,
which displayed no deactivation for 144 h. Hydrogen yield was also higher, at
381 μmol/min for modified catalyst in comparison with 334 μmol/min for unmodified one. Roy et al. [303] attributed the superior performance of plasma-treated catalyst to an increase in Ni metal dispersion, stronger metal-support interaction and
increase in acidity. Detailed studies on the influence of preparation methods for Ni/
Al 2 O 3 [304, 305] and Ru/TiO 2 [306] catalysts on the performance for ethanol
reforming process have also been reported. Nickel supported on Mg-Al hydrotalcites with basic character and higher surface area and pore volume displays
higher ethanol reforming activity compared to Ni/Al 2 O 3 [307]. Though n-butanol
has higher hydrogen content (13.5% w/w) compared to ethanol (13%) and methanol
(12.5%), n-butanol conversions are low, 5.77% on Ni/CeO 2 and 2.77% on Ni/Al 2 O 3
at 488 K [308]. Both noble metal (Pt, Pd) and non-noble metal (Ni) catalysts have
been explored for reforming of sorbitol and xylitol [289]. Higher hydrogen yield
and hydrogen selectivity were observed for xylitol in comparison with sorbitol,
since its longer carbon chain leads to higher alkane formation.
Comparative evaluation of the APR activity of different alcohols has been
reported albeit with some contradictions. While Shabaker et al. [309] reported similar APR rates for methanol and ethylene glycol on Pt/Al 2 O 3 , with higher hydrogen
production rate for methanol, Liu et al. [310] reported higher ethylene glycol
reforming rates with higher hydrogen selectivity compared to methanol, on Pt catalysts on five different supports.
According to Cortright et al. [283], amongst different alcohols, maximum selectivity for hydrogen production was observed with methanol, with lowest CO 2 production, since it has lowest number of carbon atoms (Table 7).
These studies reveal that C-C bond cleavage is not the decisive step in APR process and the reaction mechanism varies with the type and molecular structure of the
substrate alcohol.
R. Vinayagamoorthi et al.