Acid properties of SBA-15 and sol-gel ZrO2 modified using phosphate ions
that it possesses only one-fifth the specific surface area of the SBA-15 catalysts.
José I. Martínez-Martínez1, Karina Cruz-Rodríguez1, Brent E. Handy1, Ricardo GarcíaAlamilla2
1
Universidad Autónoma de San Luis Potosí, Facultad de Ciencias Químicas, San Luis Potosí,
SLP 78210 (México)
2
Instituto Tecnológico de Ciudad Madero, División de Estudios de Posgrado e Investigación,
Ciudad Madero, Tamaulipas, 89440, México
*handy@uaslp.mx
Introduction
A recent effort in catalysis is to consider production of existing petrochemical
products and alternative fuels from non-petroleum feedstocks. Zirconium oxide (ZrO2) has
been widely studied because of its catalytic behavior for converting organic molecules (i.e.,
alcohol dehydration) to obtain high value-added compounds and ethers as alternative fuels [13]. Used in combination with SBA-15, the ZrO2-SBA system can promote the development of
particular acid sites tailored for a specific reaction. The acidic properties of these materials can
be improved by incorporating some dopants or impurities on the specific surface [4]. In this
work, phosphate ions from phosphoric acid and diammonium hydrogenphosphate were used to
improve the catalytic properties of both ZrO2 and SBA-15, providing similar acid properties as
could formerly only be attained using expensive elements (Pd, Pt). Catalysts prepared here
have potential for use in phenol hydrodeoxygenation (HDO) reactions, to be used in
conjunction with phenolic compounds that arrise from lignocellulosic transformation
processes.
Materials and Methods
ZrO2 materials were prepared via sol-gel method using zirconium butoxide, 2propanol, and distilled water. The dried powder obtained was calcined at 600 °C for 3 h (SGZrO2). PO43– ions were incorporated by adding the appropriate amount of H3PO4 solution and
subsequent calcination at 600 °C for 3 h. SBA-15 catalysts were prepared using a previously
reported procedure [5], as well as the steps for zirconia and phosphate incorporation into SBA15 [6], in brief, an amount of ZrOCl2·8H2O was added to achieve 1 mol % Zr per mol silica
(sample designated Z/SBA-15). For the phosphorus-containing catalyst, a portion of the
Z/ZBA-15 sample was mixed with a solution of ((NH4)2HPO4) to obtain 9 mol% P per mol
silica (sample designated PZ/SBA15). Textural and structural properties were characterized by
BET and XRD. Acidic properties were characterized by potentiometric titration technique with
n-butylamine, and the 2-propanol dehydration test reaction (100 mg catalyst, N2 flow at 40 mL
min–1 saturated with 2-propanol at 10°C to give 2-propanol mass flowrate = 0.5 g h–1).
Results and Discussion
XRD patterns (Figure 1) show that the crystallinity of SBA-15 was not affected by phosphate
incorporation, yet unlike pure zirconia, the P/ZrO2 was non-crystalline with greatly increased
specific surface area. All prepared samples were non-microporous as determined by BET and
t-plot analysis (isotherms not shown) and both Z/SBA-15 and PZ/SBA15 maintained pore
characteristics similar to pure SBA-15 (Table 1). The maximum acid strength result for P/ZrO2
is indicative of its superior acidity and explains the 100% 2-propanol conversion, considering
Figure 1. XRD patterns of a) SBA-15 samples, b) ZrO2 samples
More comparative reaction studies are in progress to confirm these results at the same reaction
temperatures. Nevertheless, the utility of phosphate incorporation is clearly demonstrated and
should in general apply to other organic oxygenated molecules. Important catalytic steps to
facilitate hydrogenation in certain hydrodeoxygenation reactions are promoted by enhanced
acidity [7].
Table 1. Textural and acid properties of the synthesized catalysts.
Reaction
Maximun
Specific
Conversion
Sample
Temperature
Acid Strength
Surface
(%)
(°C)
(mV)
(m2/g)
SG ZrO2
360
43
-140
10
P/ZrO2
360
100
230
170
SBA-15
180
0
-9
795
Z/SBA-15
180
21
113
875
PZ/SBA15
180
23
163
800
Significance
Acid properties of all synthesized catalysts were improved by adding phosphate ions. The
results of this work indicate that modified Zr/SBA catalysts have many possibilities to obtain
good performance in transforming organic oxygenated molecules.
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