547
glycol and glycerol, has been investigated extensively, and comprehensive reviews
covering noble (Pt) and non-noble (Ni) monometallic and bimetallic (Pt-Re, Pt-Mn,
Pt-Ni and Ni-Sn) catalysts on various supports and the influence of process conditions have been published [287, 289].
In the case of ethylene glycol, the order of activity on silica-supported metal
catalysts was observed to be Pt ~ Ni > Ru > Rh > Pd > Ir, with Pt and Pd displaying
high selectivity for H 2 formation while Ni and Rh for alkanes [288]. Amongst the
supports investigated, alumina, silica, activated carbon (AC), mesoporous carbon
(CMK-3) and pseudo-boehmite (Catapal B) for monometallic Pt and bimetallic
Pt-Re and Pt-Mn catalysts [290–292], CMK-3 and AC exhibited higher conversion
and selectivity for H 2 and better hydrothermal stability compared to silica and alumina supports. Kim et al. [291] have investigated several bimetallic catalysts supported on CMK-3 and observed that Pt-Re displayed high conversion (44.2%) but
higher alkane selectivity (19.8%), while Pt-Mn exhibited lower conversion (39.7%)
and lower alkane selectivity (2.9%) with higher hydrogen production rate,
26.8 cm
3
/g/min vis-à-vis 19.8 cm
3
/g/min for Pt-Re catalyst. Higher activity observed
with bimetallic Pt-Mn and Pt-Ni catalysts is attributed to alloy formation [291, 293].
According to Bai et al. [294], addition of basic components, MgO and CeO 2 , to
alumina-supported Pt-Re catalysts resulted in 100% conversion and nearly 100% H 2
selectivity. Increase in Pt dispersion by addition of CeO 2 and moderation of alumina
acidity by MgO are proposed to be responsible for high activity and selectivity.
Choice of support, tuning support characteristics, metal loading and the active phase
composition are thus crucial to achieve higher conversion as well as selectivity.
Similar studies on supported metal catalysts, especially on Pt-based mono- and
bimetallic catalysts, on different supports, have been reported for aqueous phase
reforming of glycerol as well [287, 289]. One significant observation [295, 296] is
that larger Pt particles lead to a decrease in H 2 and CO 2 formation and C-C bond
cleavage is favoured by small Pt particles as against C-O bond cleavage and hydrogenation reactions, thus highlighting the importance of catalyst preparation methods to achieve higher metal dispersion. Though nickel-based mono- and bimetallic
(Pt-Ni) catalysts were active for APR of glycerol, deactivation of catalysts was a
major concern, and several strategies, like changes in method of preparation (solgel, combustion synthesis), choice of supports and promoter elements, have been
adopted to improve the stability of the catalyst [289]. Wen et al. [297] observed that
for Pt-based catalysts, basic supports (MgO, CeO 2 ) resulted in higher conversion
and selectivity, while neutral (AC) and acidic supports (alumina, silica, HUSY)
increased the formation of alkanes. An exhaustive review by Fasolini et al. [298]
covering the catalysts and process features in steam reforming and aqueous phase
reforming of glycerol brings out the latest developments on these two processes.
Highly efficient catalysts for both glycerol steam reforming (Ni/La 2 O 3 -Al 2 O 3 catalyst with 100% conversion and 99.7% H 2 yield [299]) and aqueous phase reforming
(Pt-Ni-Ce/Al 2 O 3 catalyst with 96% conversion and 96% yield [300]) have been
reported.
Though many methods for reforming of ethanol like steam reforming, oxidative
reforming and autothermal catalytic reforming are known, all of them involve
Catalytic Conversion of Alcohols into Value-Added Products
glycol and glycerol, has been investigated extensively, and comprehensive reviews
covering noble (Pt) and non-noble (Ni) monometallic and bimetallic (Pt-Re, Pt-Mn,
Pt-Ni and Ni-Sn) catalysts on various supports and the influence of process conditions have been published [287, 289].
In the case of ethylene glycol, the order of activity on silica-supported metal
catalysts was observed to be Pt ~ Ni > Ru > Rh > Pd > Ir, with Pt and Pd displaying
high selectivity for H 2 formation while Ni and Rh for alkanes [288]. Amongst the
supports investigated, alumina, silica, activated carbon (AC), mesoporous carbon
(CMK-3) and pseudo-boehmite (Catapal B) for monometallic Pt and bimetallic
Pt-Re and Pt-Mn catalysts [290–292], CMK-3 and AC exhibited higher conversion
and selectivity for H 2 and better hydrothermal stability compared to silica and alumina supports. Kim et al. [291] have investigated several bimetallic catalysts supported on CMK-3 and observed that Pt-Re displayed high conversion (44.2%) but
higher alkane selectivity (19.8%), while Pt-Mn exhibited lower conversion (39.7%)
and lower alkane selectivity (2.9%) with higher hydrogen production rate,
26.8 cm
3
/g/min vis-à-vis 19.8 cm
3
/g/min for Pt-Re catalyst. Higher activity observed
with bimetallic Pt-Mn and Pt-Ni catalysts is attributed to alloy formation [291, 293].
According to Bai et al. [294], addition of basic components, MgO and CeO 2 , to
alumina-supported Pt-Re catalysts resulted in 100% conversion and nearly 100% H 2
selectivity. Increase in Pt dispersion by addition of CeO 2 and moderation of alumina
acidity by MgO are proposed to be responsible for high activity and selectivity.
Choice of support, tuning support characteristics, metal loading and the active phase
composition are thus crucial to achieve higher conversion as well as selectivity.
Similar studies on supported metal catalysts, especially on Pt-based mono- and
bimetallic catalysts, on different supports, have been reported for aqueous phase
reforming of glycerol as well [287, 289]. One significant observation [295, 296] is
that larger Pt particles lead to a decrease in H 2 and CO 2 formation and C-C bond
cleavage is favoured by small Pt particles as against C-O bond cleavage and hydrogenation reactions, thus highlighting the importance of catalyst preparation methods to achieve higher metal dispersion. Though nickel-based mono- and bimetallic
(Pt-Ni) catalysts were active for APR of glycerol, deactivation of catalysts was a
major concern, and several strategies, like changes in method of preparation (solgel, combustion synthesis), choice of supports and promoter elements, have been
adopted to improve the stability of the catalyst [289]. Wen et al. [297] observed that
for Pt-based catalysts, basic supports (MgO, CeO 2 ) resulted in higher conversion
and selectivity, while neutral (AC) and acidic supports (alumina, silica, HUSY)
increased the formation of alkanes. An exhaustive review by Fasolini et al. [298]
covering the catalysts and process features in steam reforming and aqueous phase
reforming of glycerol brings out the latest developments on these two processes.
Highly efficient catalysts for both glycerol steam reforming (Ni/La 2 O 3 -Al 2 O 3 catalyst with 100% conversion and 99.7% H 2 yield [299]) and aqueous phase reforming
(Pt-Ni-Ce/Al 2 O 3 catalyst with 96% conversion and 96% yield [300]) have been
reported.
Though many methods for reforming of ethanol like steam reforming, oxidative
reforming and autothermal catalytic reforming are known, all of them involve
Catalytic Conversion of Alcohols into Value-Added Products