(769d) Crotonaldehyde Hydrogenation in a Solid-Polymer-Electrolyte Reactor

Solid-polymer-electrolyte
(SPE) reactors, with structures that are similar to those of
proton-exchange-membrane fuel cells, have been used in several recent studies to
perform chemoselective hydrogenations of multifunctional organics [1-3]. 
These reactions produce a number of value-added fine chemicals [4]. SPE reactors
can achieve superior selectivities to the desired products compared to conventional
thermocatalytic reactors [3,5]. In addition, they allow the reactions to be
carried out at moderate temperatures and pressures. Furthermore, mass transport
limitations for hydrogen can be significantly reduced via the use of proton-exchange
membrane in these reactors. These advantages have made SPE reactors promising
for the synthesis of fine chemicals.

There are limited
reports in the literature of hydrogenation reactions performed in SPE reactors.
This talk will examine the use of crotonaldehyde (CH3-CH=CH-CHO) as a probe
molecule to study the selective hydrogenation of alpha,beta-unsaturated
aldehydes, commonly used in pharmaceutical and cosmetics industries [6].

The talk will discuss
the effect of applied potential on the reaction activities and selectivies at
potentials from 0 to 1.0V. In these investigations, FKB (FuMA-Tech)
proton-exchange membrane was used with Pt/C as the electrocatalyst.  Figure
1 shows the formation rates of the hydrogenation products, crotyl alcohol and
1-butanol. The reaction rate increased with increasing applied potential from 0
- 0.5V then remained constant for potentials higher than 0.5 V. The best result
was achieved at 1.0 V (selectivity toward crotyl alcohol of up to 33%). This
level of performance is comparable to the average selectivity (45%) obtained
from the thermocatalytic process [7-8].  The talk will also elucidate the
reaction pathways for the hydrogenation of crotonaldehyde and its
intermediates. This will be accomplished by analyzing the reaction rates for
each elementary step in crotonaldehyde hydrogenation as illustrated in Figure 2.

Figure 1:
Formation rates of hydrogenation products as a function of the applied
potential. FKB (FuMA-Tech) proton-exchange membrane, 20% Pt/C as electrocatalysts,
room temperature, and 1 atm H_2.

Figure 2: Elementary
steps in crotonaldehyde hydrogenation, k₁-k₅
forward reaction rate constants; k_-1-k_-5 reversed
reaction rate constants.

REFERENCES

1.     
Ogum
Z, Nishio K, Yoshizawa (1981) Ibid 26:1779

2.      An
W, Hong JK, Pintauro PN, Warner K, Neff W (1988) J Am Oil Chem Soc 75:917

3.      Yuan
XZ, Ma ZF, Jiang QZ, Wu WS (2001) Electrochem Commu 3:599

4.      Blaser HU, Malan C,
Pugin B, Spindler F, Steiner H, Studer M (2003) Adv Synth &
Catal 345:103

5.      Pintauro
PN (2005) Ind Eng Chem Res 44:6188

6.      Claus
P (1988) Topics in Catalysis 5:51

7.      Campo
B, Santori G, Petit C, Volpe M (2009) Applied Catalysis A: General  359:79

8.      Yang
X, Wang A, Wang X, Zhang T, Han K, Li J (2009) J. Phys. Chem. C  113:
20918