Photon Factory Activity Report 2016 #34 (2017)

BL-9C/2015G712

EXAFS analysis for Cu nanocatalysts active for transfer hydrogenation of α,βunsaturated carbonyl compounds
Rajaram Bal1,* and Takehiko Sasaki2
1
Refinery Technology Division, CSIR- Indian Institute of Petroleum,
Dehradun-248005, India
2
Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kaswhianoha, Kashiwa,Chiba, 277-8561, Japan
1 Introduction
The selective hydrogenation of α, β Unsaturated
aldehydes and ketones to corresponding unsaturated
alcohols is of paramount importance in organic synthesis.
These unsaturated alcohols are intermediates used in theproduction of foods, pharmaceuticals and cosmetics. The
hydrogen addition to the conjugated C=C bond in an α,βunsaturated carbonyl compounds is both kinetically andthermodynamically favoured over C=O. Therefore
research efforts have been made for improving theselectivity of unsaturated alcohols. We report here thepreparationofCu-nanoparticles
supportedon
nanocrystalline MgO for selective hydrogenation of α,βunsaturated carbonyls compounds to corresponding α,βunsaturated alcohols via sonication method and thisprepared catalyst is highly active for the chemo-selective
transfer hydrogenation of α, β unsaturated carbonylcompounds to corresponding α,β-unsaturated alcohols. To
best of our knowledge there is no report in the open
literature where a single heterogeneous catalyst is used
for the dehydrogenation of cyclohexanol tocyclohexanone where this in-situ generated hydrogen isused for selective hydrogenation of α,β unsaturated
aldehydes and ketones to unsaturated alcohols. Cu Kedge EXAFS measurements were conducted for the
structural characterization for the fresh and the spent
catalysts.
2 ExperimentWell dispersed nanocrystalline copper oxide supported
on magnesia (Cu/MgO) was prepared by simple ultrasonication assisted synthesis procedure. Starting materials
were Mg(NO3)2.6H2O and Cu(NO3)2.2.5H2O.
The
detailed procedure will be reported elsewhere. The
obtained catalyst was found to be the active catalyst forthe chemoselective transfer hydrogenation of unsaturated
carbonyl compounds to produce corresponding alcohols
with very high yield. Transfer hydrogenation of
cyclohexanol
andcinnamaldehyde
produce
cyclohexanone and cinnamyl alcohol with 100%
selectivity.
EXAFS measurements of Cu-K edge were carried out
at KEK-IMMS-PF BL9C.
3 Results and Discussion
Cu K-edge EXAFS measurements were conducted forthe structural characterization for the fresh and the spent
catalysts as shown in Fig. 1. The curve fitting results aresummarizedinTable 1. The
fresh and spent
5%Cu-MgO
catalysts
show
the presence ofCuO (as Cu-Opath) clusters. In
addition,thespent
catalyst
showedtheformationofmetallic Cu (asCu-Cupath)clusters and webelieved that thismetallicCunanoclusters
speciesaretheactivespeciesfor thisFig. 1: k3-weighted Cu K-edge EXAFS
Fourier transforms and curve fitting results
for the fresh (upper) and the spent (lower)
Cu/MgO catalyst

reaction.
The Cu–O coordination number (CN) in the freshcatalyst was 2.0±0.4 and the Cu–O distance was1.958±0.012Å, which is similar to the bond length ofCuO oxide. The small CN of Cu–O indicates theformation of nanosized CuO on the MgO surface. The
EXAFS data for the spent catalyst indicate no significant
change in CuO structures during the catalytic reaction.
Table 1: Summary of the EXAFS fitting results for thefresh and spent Cu catalystsa
PathR (10- nm)

1CN

DW (102nm )E0(eV)

Rf(%)

Fresh

Cu-O

1.958±0.012

2.0±0.4

1.8±1.7-5.0±2.9

1.2Spent

Cu-O

1.932±0.032

0.6±0.7

0.6±6.3-11.2±3.7

8.6

Cu-Cu

2.553±0.023

8.3±2.915.3±3.1

5−1a−1Fitting was conducted in the range Δk: 3–13 (10 nm) and ΔR: 1.2–2.8 (102nm). Amplitude reducing factor S0 was set as 0.95

* raja@iip.res.in