Y. Wang et al.
Applied Catalysis A, General 550 (2018) 214–227
pure glycerol in chemicals, pharmaceuticals and cosmetics, the re-
utilization of by-product glycerol is limited, due to it comprises several
other impurities (such as inorganic salts, methanol, free fatty acids,
methyl esters, un-reacted reactants and a plenty of water) [9,10].
Therefore, it has high toxicity and low commercial value, and further
refining is expensive, tasteless but wasteful to discard [11].
In order to take full advantage of by-product glycerol, which is also
prepared from the hydrogenolysis of sorbitol [12] or the fermentation
of glucose [13] and obtained as a co-product in lignocellulose-to-
ethanol conversion [14] or soap manufacture [15], it can be employed
for producing hydrogen. Hydrogen is always considered as a clean
energy source and favorable raw materials for chemical synthesis, and
then its demand would be expected to significantly increase in the fu-
ture, since the technological advancements during the fuel cell and
ammonia synthesis industries [16–18]. Glycerol is a good substitution
for producing hydrogen in comparison with methanol and ethanol,
mainly due to it does not make the Nafion membrane swell in PEMFC
conducted the GSR experiment over different noble metals (Pt, Ir, Pd
and Ru) promoted Ni/CeO
strated the addition of noble metals all increased the H
glycerol conversion accompanied with the increase of CH yield.
2
Among them Ni-Pt/CeO -Al catalyst showed the highest H yield
2
-Al
2
O
3
catalysts, and their results demon-
2
yield and
4
2
2
O
3
and the lowest coke deposition rate. In spite of the noble-metal-based
catalysts presented more active and more stable during GSR, their high
expense virtually restrains their application on an industrial scale.
In order to realize the economical efficiency of catalysts applied for
GSR reaction, the lion’s share of researchers have shifted their interests
to transition-metal-based catalysts, such as Ni-, and Co-based catalysts
[8,21,33,46–53]. Among them, nickel-based catalysts were widely
studied in GSR reaction and stand as one of the most investigated ones
so far, which mainly due to its high capacity of breaking CeC bonds and
lower cost. However, nickel species as active phase are easily sintered
and Ni-based catalysts always present high carbon deposition rate, re-
sulting in a dramatic deactivation on GSR process [21]. Wu et al. [48]
[
19]. In present, the technologies of hydrogen production from glycerol
prepared perovskite-derived nickel-based catalysts (La1–xCa
x = 0.0, 0.1, 0.3, 0.5, 0.7 and 1.0) and investigated their catalytic
performance on GSR reaction. The La0.5Ca0.5NiO catalyst showed the
highest H yield and lower amount of coke deposition, owing to its
strongest metal-support interaction (MSI) and best metal dispersion,
while its stability significantly diminished after 15 h on steam. In ad-
x 3
NiO ,
mainly though the catalytic reactions, such as steam reforming [20–24],
aqueous phase reforming [25], auto-thermal reforming [26,27], and
supercritical water reforming [28,29]. Among them, hydrogen pro-
duction from glycerol steam reforming (GSR) is attractive because
every mole of glycerol participated in reaction can theoretically gen-
erate seven moles of hydrogen according to Eq. (1). As is known to all,
the GSR reaction is always carried out at high temperature (> 400 °C),
thus the decomposition of glycerol (Eq. (2)) is ineluctably happened
and the produced carbon monoxide will react with steam to form water-
gas shift reaction (WGSR) (Eq. (3)), which is considered as effective for
hydrogen production in steam reforming reaction (SRR) [8,30]. In ad-
dition, there are also some other side reactions, such as methane steam
and dry reforming (Eq. (4)–(6)), and a series of coke formation reac-
tions (Eq. (7)–(9)) based on employing different catalysts and operating
conditions [21,31–33].
3
2
dition, Ni/La
accompanied with the higher CO
modified Ni/Al catalysts during the GSR reaction at 400 °C, but it
2
O
3
-Al
2
O
3
catalysts presented the highest H
2
yield (47%)
2
yield (59%) in B
2
O
3
and La O
2 3
2 3
O
exhibited dramatic deactivation after 18 h of reaction and about
200 mg/gcat. of total carbon deposition [33].
So as to overcome these major drawbacks, some studies have been
done to exploit and design more suitable nickel-based catalysts. Some
supports with unique textural properties (such as higher surface area
and larger pore volume) and meso-structure, e.g. SBA-15 [54], SiO
[55] and ZrO [56], have been employed for preparing Ni-based cata-
2
2
lysts. This is attributed to these distinctive properties are capable of
highly dispersing active phase (Ni ) and forming the strong interaction
0
C
3
3
H
H
8
8
O
3
+ 3H
2
O → 3CO
2
+ 7H
2
∆H = 123 kJ/mol
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
o
C
O
3
→ CO, CO
2
, CH
4
, H
2
with nickel species, which are widely regarded as important for su-
perior catalytic activity and stability [57]. Apart from that, the Ni-based
catalysts usually combined with other second metals, such as Pt [58],
Co [59,60], Cu [24,49,61], and Cr [62] have also been investigated
during GSR reaction and the results according to literatures demon-
strated Ni-based bimetallic catalysts effectively suppressed the sintering
of nickel species by forming metal alloy, and then leaded to the long-
term catalytic stability. Cheng and his co-works [59,60] investigated
the nature of coke formation on bimetallic Co-Ni/Al O catalyst during
0
CO + H2O ↔ CO2 + H2 ∆H = −41 kJ/mol
0
CH4 + H2O ↔ CO + 3H2 ∆H = 206 kJ/mol
0
CH4 + 2H2O ↔ CO2 + 4H2 ∆H = 165 kJ/mol
0
CH4 + CO2 ↔ 2CO + 2H2 ∆H = 274kJ/mol
0
2
CO ↔ CO2 + C ∆H = 172 kJ/mol
2 3
GSR reaction at 500 °C and 550 °C was attributed to the various glycerol
dissociative adsorption and steam molecular chemisorption on two
different sites of catalyst surface at different steam-to-glycerol ratios.
This was related to the presence of both basic sites and Brönsted acid on
0
CH4 ↔ 2H2 + C ∆H = 75.6 kJ/mol
0
CO + H2 ↔ H2O + C ∆H = 131 kJ/mol
For the catalysts applied into GSR, the research hotspots principally
focus on the catalysts that have superior ability of breaking the CeC,
CeH and OeH bonds and maintaining the CeO ones, resulting in ob-
the catalyst. The Ni-Cu/Al
GSR by Wang et al. [61], it exhibited significantly higher H
2
O
3
catalyst was prepared and applied into
selectivity
2
(92.9%) and glycerol conversion (90.9%) at 650 °C in comparison with
those of Ni/MgO. In addition, Carrero et al. [62] compared the catalytic
performance of bimetallic Ni-(Cu, Co, Cr)/SBA-15 Silica catalysts on
GSR reaction at 600 °C. It was observed that the glycerol conversions
over different catalysts as the following order: Ni-Cr/SBA-15 > Ni-Co/
2 4
tain higher H selectivity and lower CH selectivity [30,32,34]. Herein,
a large number of scholars have bent themselves to develop catalysts
based on monometallic and bimetallic systems supported on various un-
modified and/or modified metal oxides carriers. Obviously, the noble
metals, such as Pt [35–37], Pd [38], Rh [39,40], Ru [41,42] and Ir [38],
and bimetallic systems that combined with transition metals [43–45],
have obtained considerable attentions, due to their predominant feed-
stock conversion, high selectivity for target product and exceptional
stability. Pompeo et al. [37] reported the GSR reaction over Pt sup-
ported different carriers (such as SiO
modified with Ce and Zr, respectively) for obtaining hydrogen/synth-
esis gas at low temperatures (< 450 °C), indicating that Pt/SiO catalyst
exhibited a promising ability for dehydrogenation reactions and CeC
bonds cleavage and superior stability during 40 h of reaction. As has
been taken into account in literature [44], Profeti and his co-workers
SBA-15 > Ni/SBA-15 > Ni-Cu/SBA-15, and the corresponding H
2
distributions with the sequence: Ni-Cr/SBA-15 > Ni/SBA-15 > Ni-
Co/SBA-15 > Ni-Cu/SBA-15. Additionally, the Ni-Cr/SBA-15 ex-
hibited the excellent stability for 60 h on stream reaction and lowest
carbon deposition rate (13 mgcoke/(gcat h)). Therefore, the application
of Ni-based bimetallic catalysts and supports with unique textural
properties into catalytic systems for GSR reaction is a promising and
potential technique to promote the product selectivities, glycerol con-
versions and catalytic stabilities of Ni-based catalysts.
2 2
, γ-Al O
3
, ZrO
2
, and α-Al
2 3
O
2
Attapulgite (ATP, it is often called as palygorskite) is a kind of hy-
drated
magnesium
aluminum
silicate
clay
mineral
215