Please donot adjust the margins
and many other petrochemical products [1, 2]. In current world market, 1,3-butadiene is mainly produced by separating from the C4
fraction following ethylene manufacturing via the steam cracking of naphtha. However, its production is largely tied with the
petroleum resources.
With the advancement of bioethanol technology and abundant ethanol source in recent years, synthesizing 1,3-butadiene from
renewable ethanol draws great interests [3, 4]. The synthesis of 1,3-butadiene from ethanol have two major routes: one-step direct
synthesis of 1,3-butadiene and two-step production process (ethanol is first partially converted to acetaldehyde and acetaldehyde is
further reacted with ethanol to obtain 1,3-butadiene) [1, 5, 6]. The two-step process has advantages of low reaction temperature and
high selectivity to 1,3-butadiene, but the process is more complicated and the equipment investment is higher in comparison with one-
step method. For one-step process, how to fabricate an efficient catalyst with high 1,3-butadiene selectivity is always a big challenge.
The reaction mechanism of this system is complicated and involves five consecutive reaction steps (Scheme 1) [7, 8]: (i) ethanol is
dehydrogenated to acetaldehyde, (ii) two acetaldehyde molecules are converted to acetaldol by aldol-condensation, (iii) acetaldol is
dehydrated to form crotonaldehyde, (iv) Meerwein–Ponndorf–Verley (MPV) reaction between crotonaldehyde and ethanol to obtain
crotyl alcohol, (v) 1,3-butadiene is generated by the dehydration of crotyl alcohol. In this multiple-step reaction system, ethanol
dehydrogenation and aldol-condensation are two critical steps [9], which require two different active sites of the catalyst. For ethanol
dehydrogenation, redox active sites are required, typically provided by copper oxide [1, 5, 8], silver [1, 10] or zinc oxide [1, 11]. The
aldol-condensation reaction requires Lewis acid or base sites. The Lewis acid sites are generally supplied by elements from the IIIB,
IVB and VB groups in the periodic table, such as Y [12], Zr [13], Hf [14] and Ta [15]. Magnesium oxide is the typical candidate for
Lewis base sites [16]. An excellent ethanol-to-1,3-butadiene catalyst requires wise coupling of these two types of active sites.
Baerdemaeker et al. developed a stable and active catalyst by combining Hf(IV) with Zn(II), in which the adding of Zn(II) to the
Hf(IV)-containing catalyst was crucial important to force the Hf(IV) into catalyzing the acetaldehyde condensation rather than the
ethanol dehydration [17]. Dai et al. prepared a bi-component Zn−Y catalyst confined in zeolite cages, and exhibited a high 1,3-
butadiene selectivity of 63% in the one-step process [18].
Scheme 1. Reaction mechanism of ethanol to 1,3-butadiene.
Ordered mesoporous silica (OMS) materials, such as SBA-15 [19], KIT-6 [19], MCF [20] and MCM-41 [21], were explored as
catalyst supports in this reaction system. Their large pore size and specific surface area were believed to improve the accessibility of
active sites for reactants and intermediates, effectively solving the mass transfer and coking formation during 1,3-butadiene production
from ethanol [19]. Chae et al. have reported that Ta/OMS catalysts had better coke tolerance, catalytic longevity and catalytic activity
than conventional silica-based catalysts [19]. For these catalysts, the metal was generally loaded by wet impregnation method, which
was not time and energy effective. However, solvent-free method has not yet reported in the ethanol to 1,3-butadiene system.
2
In this study, we compared two kind of ZnO-CeO /SBA-15 catalysts with different solid-state grinding method (SBA-15 with or
without organic template P123 (PEO-PPO-PEO) during grinding process). The limited space between the template P123 and the silica
wall of SBA-15 prevents the infiltrated metal oxides from forming large aggregates, and achieving a high dispersion of oxides. The
effect of the template P123 in SBA-15 on the formation process and physicochemical properties of the catalysts, as well as the catalytic
performance in ethanol-to-1,3-butadiene were discussed in detail. In addition, as a solvent-free method, this solid-state grinding
strategy is energy effectively and environmentally friendly in comparison with wet impregnation method.
The mesoporous silica SBA-15 support was prepared by a hydrothermal synthesis method reported by Zhao et al. [22] The as-
prepared SBA-15 material (with organic template) was recovered by filtration, washed and dried. Then through calcination, the
1 5 1 5
template-free SBA-15 material was obtained. The catalysts 10Zn Ce -AS/10Zn Ce -CS were prepared by solid-state grinding the as-
prepared/template-free SBA-15 with the metal precursors. 10Zn-AS and 10Ce-AS were only loaded single metal oxide. The detailed
information about synthesis method was given in Supporting information.
In order to explore the decomposition process of catalysts, the as-prepared SBA-15, 10Zn
characterized by TG technique. As shown in Fig. 1a, the decomposition of template (P123) of as-prepared SBA-15 takes place between
50 °C and 280 °C, corresponding to a sharp DTG peak at 180 °C in Fig. 1b. As the temperature further rises, the subsequent weight
loss is attributed to the removal of residual carbonaceous species [23]. The decomposition of 10Zn Ce -CS presents two DTG peaks at
0 °C and 200 °C, which is the result of the removal of water and the thermal decomposition of Zn(NO and Ce(NO , respectively.
For 10Zn Ce -AS, the TG curve shows 50% weight loss due to the decomposition of organic template and metal salt precursors.
1 5 1 5
Ce -AS and 10Zn Ce -CS were
1
1
5
8
3
)
2
3 3
)
1
5
However, the decomposition temperature of P123 is at around 235 °C, much higher than that for SBA-15 support itself (180 °C) [22].
Similar phenomenon has also been observed on CuO/SBA-15 [24] and ZnO/SBA-15 [25]. This is believed as the result of the strong