(292e) Fine Tuning of the Acid/Base Properties of Pt/Alumina for Enantioselective Reactions | AIChE

(292e) Fine Tuning of the Acid/Base Properties of Pt/Alumina for Enantioselective Reactions

Authors 

Baiker, A. - Presenter, ETH Zürich
Pratsinis, S. E. - Presenter, Swiss Federal Institute of Technology, Particle Technology Laboratory, ETH Zurich
Mallat, T. - Presenter, ETH Zürich
Hoxha, F. - Presenter, ETH Zürich
Krumeich, F. - Presenter, Particle Technology Laboratory, ETH Zurich


The acid/base
properties of Pt/Al2O3 were modified by doping the
support with SiO2 or Cs2O and the catalysts were prepared
by flame spray pyrolysis in a rapid, single step process with excellent
reproducibility. The catalysts contained 4.7 wt.% Pt and the support
composition varied in the range 0-100 wt.% SiO2 or 0-10 wt.% Cs2O.
Up to 50 wt.% SiO2 the BET surface areas could be kept in a narrow
range (141±15 m2g-1), while higher SiO2 content
increased the surface area and diminished the crystallinity of the support. CO
chemisorption and XRD showed a positive correlation between the SiO2
content and the size of the dominantly spherical Pt particles. The catalysts
containing 22-30 wt.% SiO2 were the most acidic as evidenced by TPD
of NH3. In the hydrogenation of acetophenone the SiO2-doped
catalysts were highly active and the selectivity to the hydrogenolysis
byproducts increased with increasing SiO2-content by more than
20-fold. This is a confirmation of the effect of support acidity on the
properties of the Pt-H system. On the other hand, addition of Cs2O barely
affected the Pt particle size and TPD of CO2 confirmed the increase of
surface basicity with increasing Cs2O content. Cs2O was probably
enriched at the Al2O3 surface and strongly influenced the
acid/base properties and thus the catalytic performance already at very low
concentrations. Only 0.25 wt.% Cs2O blocked the hydrogenolysis of 1-phenylethanol
to ethylbenzene.

Additonally the
influence of support acidity and basicity was investigated in the enantioselective
hydrogenation of methyl benzoylformate and ketopantolactone on
cinchonidine?modified catalysts. Addition of SiO2 improved the
enantioselectivity with a maximum at 30 wt.%. Enantioselectivity correlated
well with the acidity of the catalysts characterized by TPD of NH3 and with the
selectivity to hydrogenolysis of methyl cyclohexyl ketone to ethylcyclohexane.
On the contrary, doping with Cs was detrimental to the formation of the
(R)-alcohols and the drop in enantioselectivity could unambiguously be
attributed to the basicity of the support characterized by TPD of CO2.
The practical importance of our findings is demonstrated by the best ee (94 ±
0.5%) achieved so far in the industrially relevant hydrogenation of
ketopantolactone to (R)-pantolactone.

Checkout

This paper has an Extended Abstract file available; you must purchase the conference proceedings to access it.

Checkout

Do you already own this?

Pricing

Individuals

AIChE Pro Members $150.00
AIChE Graduate Student Members Free
AIChE Undergraduate Student Members Free
AIChE Explorer Members $225.00
Non-Members $225.00