Homogeneous, Heterogeneous and Nanocatalysis - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 28

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Figure 1.3 Publications on MW-assisted reactions (1990-2013). Number of articles
involving MW-assisted reactions. Scopus keyword search on 'microwave
reaction'.

reactions by MW energy has been an increasingly popular subject and a large
number of papers have been published in this field over the past 20 years
(Figure 1.3).
In many of the published studies, MW heating strongly decreased pro-
cessing times, increased product yields and increased product purity, com-
pared with conventional heating methods. 145-149 The nature of the MW
enhancement is usually attributed to several specific thermal effects that
cannot be emulated by conventional heating methods, such as the rapid
heating rate, the prevention of thermal wall effects and the selective heating
of particular reaction components and/or intermediates.
More recently, the advantages of this empowering technology have been
exploited in the fields of nanomaterial synthesis 150-153 and catalysis. 154
As an example, MW effects in heterogeneous catalysis were investigated in
the dehydrogenation reaction of decalin and tetralin. 155,156 The use of MW
heating proved both to improve the reagent conversion and to lower the
deactivation rate of the catalyst. An observed beneficial effect of MW use was
the large temperature gradient between the catalyst and surrounding species
(direction of heat transfer reversed compared with the thermal mode). This
led to the acceleration of mass desorption and species transport in the
system, reduction of coke deposition and enhancement of tetralin de-
hydrogenation. Nevertheless, evidence of the MW effect was only observed in
reactions controlled by mass transfer as the rate-limiting step.
Supported iron oxide nanoparticles on aluminosilicate catalysts were
found to be e cient and easily recoverable materials in the aqueous se-
lective oxidation of alcohols to their corresponding carbonyl compounds
under both conventional and microwave heating. 157 The use of catalysis in

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