594
due to lack of C–C bond that helps to activate it at lower temperature (300–400 °C)
compared to that of methane (>700 °C) [58]. There is an advantage of less CO and
coke formation during SRM reaction. This makes methanol a good candidate for
hydrogen production for different applications including on-board fuel cells to
power electric cars [25].
2.1 Reaction Mechanism for Steam Reforming
of Methanol (SRM)
The main methanol steam reforming is [25]:
CH 3 OH + H 2 O ↔ CO 2 + 3H 2 (ΔH = +49.7 kJ/mol).
Other side reactions are:
CH 3 OH ↔ CO + 2H 2 (ΔH = +90.2 kJ/mol) (methanol decomposition).
CO + H 2 O ↔ CO 2 + H 2 (ΔH = −41.2 kJ/mol) (water-gas shift reaction).
2CO → C + CO 2 (ΔH = −171 kJ/mol) (Boudouard reaction).
Excess amount of carbon formation is prevented by increasing the water-tomethanol molar ratio higher than the stoichiometry ratio [59]. Typically, methanol
first decomposes to give CO and H 2 . Then CO reacts with water to generate CO 2 and
H 2 via the exothermic water-gas shift reaction (shown above). Another reaction
pathway during SRM is the formation of formaldehyde due to dehydrogenation of
methanol followed by reaction of formaldehyde and water to produce formic acid.
Finally, formic acid decomposes to CO 2 and H 2 [60]. However, this reaction pathway depends on the structural and elemental composition of the catalysts.
CH 3 OH ↔ HCHO + H 2 (methanol to formaldehyde formation).
HCHO + H 2 O ↔ HCOOH + H 2 (formaldehyde to formic acid formation).
HCOOH ↔ CO 2 + H 2 (formic acid decomposition reaction).
2.2 Overview of Mesoporous Supports for Steam Reforming
of Alcohols
2.2.1 Identification of Mesoporous Structures
N 2 adsorption-desorption analysis is the most crucial characterization technique that
is widely used for mesoporous catalysts. The low-angle XRD analysis is frequently
used to confirm whether the mesoporous materials have short- or long-range ordered
mesopores. The mesostructures that have long-range ordered pores with good periodicity exhibit resolved low−/small-angle XRD diffraction peaks between 2-theta
2θ values of 2–10°, while the more amorphous inorganic frameworks which have
short-medium-range ordered pores usually show weaker intensity XRD patterns at
2θ = 20–25°. Generally, the type of isotherm and shape of hysteresis loop (based on
IUPAC nomenclature) are used to determine the morphology of mesoporous
S. Bepari et al.
due to lack of C–C bond that helps to activate it at lower temperature (300–400 °C)
compared to that of methane (>700 °C) [58]. There is an advantage of less CO and
coke formation during SRM reaction. This makes methanol a good candidate for
hydrogen production for different applications including on-board fuel cells to
power electric cars [25].
2.1 Reaction Mechanism for Steam Reforming
of Methanol (SRM)
The main methanol steam reforming is [25]:
CH 3 OH + H 2 O ↔ CO 2 + 3H 2 (ΔH = +49.7 kJ/mol).
Other side reactions are:
CH 3 OH ↔ CO + 2H 2 (ΔH = +90.2 kJ/mol) (methanol decomposition).
CO + H 2 O ↔ CO 2 + H 2 (ΔH = −41.2 kJ/mol) (water-gas shift reaction).
2CO → C + CO 2 (ΔH = −171 kJ/mol) (Boudouard reaction).
Excess amount of carbon formation is prevented by increasing the water-tomethanol molar ratio higher than the stoichiometry ratio [59]. Typically, methanol
first decomposes to give CO and H 2 . Then CO reacts with water to generate CO 2 and
H 2 via the exothermic water-gas shift reaction (shown above). Another reaction
pathway during SRM is the formation of formaldehyde due to dehydrogenation of
methanol followed by reaction of formaldehyde and water to produce formic acid.
Finally, formic acid decomposes to CO 2 and H 2 [60]. However, this reaction pathway depends on the structural and elemental composition of the catalysts.
CH 3 OH ↔ HCHO + H 2 (methanol to formaldehyde formation).
HCHO + H 2 O ↔ HCOOH + H 2 (formaldehyde to formic acid formation).
HCOOH ↔ CO 2 + H 2 (formic acid decomposition reaction).
2.2 Overview of Mesoporous Supports for Steam Reforming
of Alcohols
2.2.1 Identification of Mesoporous Structures
N 2 adsorption-desorption analysis is the most crucial characterization technique that
is widely used for mesoporous catalysts. The low-angle XRD analysis is frequently
used to confirm whether the mesoporous materials have short- or long-range ordered
mesopores. The mesostructures that have long-range ordered pores with good periodicity exhibit resolved low−/small-angle XRD diffraction peaks between 2-theta
2θ values of 2–10°, while the more amorphous inorganic frameworks which have
short-medium-range ordered pores usually show weaker intensity XRD patterns at
2θ = 20–25°. Generally, the type of isotherm and shape of hysteresis loop (based on
IUPAC nomenclature) are used to determine the morphology of mesoporous
S. Bepari et al.