ChemCatChem
10.1002/cctc.201900334
FULL PAPER
The conversion of dimethyl adipate (DMA) was evaluated using equation
Autochem II 2920 (Micromiretics, USA) connected on-line with quadrupole
mass spectrometer RGA 200 (Prevac). Quadrupole mass spectrometer
1. Due to the absence of cracking reactions (confirmed by the GC analysis
of the products), the C backbone of DMA as well as of the reaction
6
was used for monitoring of m/z = 28 (N
2 2
) and m/z = 44 (N O) signals. The
products was used as a basis for the selectivity calculation (Equation 2).
Methanol was excluded, because it was present both in the liquid and
gaseous product streams, which prevented its accurate quantification.
sample amount of 0.7 g was used. The procedure involved 1) Reduction
-
1
-1
of sample by 10 mol% H
2
/Ar (30 ml·min ) while heating 5 °C·min to
250 °C with subsequent isothermal reduction for 60 minutes at 250 °C, 2)
-
1
Desorption of hydrogen in He (30 ml·min ) at 250 °C for 30 min, 3) Cooling
ꢀ
ꢁꢂꢃ,ꢄ−ꢀꢁꢂꢃ,푡
-1
in He (30 ml·min ) to 90 °C, 4) Oxygen chemisorption in 3 mol% N
2
O/He
/Ar
°C·min-1 to 200 °C with subsequent
isothermal reduction for 30 minutes at 200 °C, 6) Desorption of hydrogen
푐표푛푣푒푟푠푖표푛퐷푀퐴
=
(1)
(2)
ꢀ
ꢁꢂꢃ,ꢄ
-
1
(
30 ml·min ) at 90 °C for 30 minutes, 5) Reduction by 10 mol% H
2
(30 ml·min ) while heating 5
-
1
ꢀ
ꢁꢂꢃ,ꢅ
푆푥 = ꢀ
ꢁꢂꢃ,푝ꢆꢇ푑푢ꢈ푡ꢉ
-
1
-1
in He (30 ml·min ) at 200 °C for 30 min, 7) Cooling in He (30 ml·min ) to
where: nDMA is number of DMA moles, i is the initial amount of moles, t is
the amount of moles at the sampling time, S is the selectivity to product x,
is number of DMA moles converted to product x, nDMA products is
-1
9
0 °C, 8) Oxygen chemisorption in 3 mol% N
2
O/He (30 ml·min ) at 90 °C
x
for 30 minutes. The copper surface area was calculated according to
procedure given in [30] and [31]. Number of atoms adsorbed on 1 m2 of
n ,
DMA x
number of DMA moles converted to all products.
2
copper surface area 0.697x1019 (at O/m Cu) and time obtained between
signals changes of N
2 2
and N O during the second chemisorption step (step
In order to compare the activity of the tested catalysts, the turnover
frequency (TOF) was calculated using equation 3.
8) were used for calculation.
ꢏꢁꢂꢃ .푥ꢁꢂꢃ
푀ꢁꢂꢃ
σꢐ푢·푁ꢃ
푇푂퐹퐶ꢊ,ꢋꢊꢌ푓푎ꢍꢎ
=
·
(3)
푚ꢐꢃꢑ·ꢒꢐ푢
Acknowledgements
-
1
where: vDMA is DMA flow rate (g.h ), xDMA is DMA conversion, MDMA is
-
1
The financial support by the Czech Science Foundation (project
No. GA17-05704S) is greatly acknowledged. Large research
infrastructure ENREGAT supported by the Ministry of Education,
Youth and Sports of the Czech Republic under project no.
LM2018098 was used to obtain Cu specific surface areas. The
authors are grateful to Josef Tomášek for technical support, Jana
Cibulková for XRD analyses, Miloslav Lhotka for nitrogen
A
molar mass of DMA (g.mol ), N is Avogadro constant, mCAT is the amount
2
-1
of catalyst (g) and SCu is specific copper area (m .g ), σCu is the cross-
2
sectional area of copper and equals 0.0154 nm .
Catalysts characterization
The phase composition of all catalysts and the size of crystallites of the
relevant phases present in the catalysts were determined by X-Ray
diffraction using a diffractometer PANanalytical X’Pert3 Powder and Cu Kα
radiation. The XRD patterns were recorded in a range of 2θ = 5 °– 70 °.
The crystallite sizes were calculated using the Scherrer’s equation.
Reflections at 2θ = 31.8°, 43.3° and 38.6° were used for the crystallite size
calculations for ZnO, Cu and CuO, respectively [27]. The copper and zinc
content of the catalyst precursors (samples with “P” ending) were analysed
by XRF using a spectrometer ARL 9400 XP equipped with a rhodium lamp.
It was assumed that the Cu/Zn ratio remained the same after calcination.
Furthermore, the absence of Cu or Zn leaching was confirmed by analysis
of the liquid products by AAS using Agilent 280FS AA, where a mixture of
acetylene and air was used as an atomization flame. Transmission
electron microscopy images, as well as element mapping resulting in the
surface composition of calcined and spent catalysts (samples with “350”
or “EX” ending), were obtained using EFTEM Jeol 2200 FS at an
accelerating voltage of 200 kV. The reducibility of the calcined and spent
catalysts was determined by Quantachrome ChemStar TPx instrument
with a TCD detector. The samples were exposed to a reducing gas mixture
2
physisorption and H -TPR analyses, Petr Sajdl for XPS analyses
and Alena Michalcová for TEM analyses.
Keywords: copper • zinc • catalyst • ester hydrogenolysis •
dimethyl adipate
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