Role of the Cu-ZrO2 Interfacial Sites for Conversion of Ethanol to Ethyl Acetate and Synthesis of Methanol from CO2 and H2

Article abstract of DOI:10.1021/acscatal.6b01805

Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO₂ on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV-vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO₂ interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N₂O chemisorption measurements. The oxidation states of the Cu and ZrO₂ species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu⁰ and Zr⁴⁺, respectively. It was found that the formation of Cu-ZrO₂ interfacial sites increased the turnover frequency by an order of magnitude in both the conversion of ethanol to ethyl acetate and the synthesis of methanol from CO₂ and H₂.

Full text of DOI:10.1021/acscatal.6b01805

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Subscriber access provided by Northern Illinois University
Article
The Role of the Cu-ZrO2 interfacial sites for Ethanol Conversion
to Ethyl Acetate and Methanol Synthesis from CO2 and H2
Insoo Ro, Yifei Liu, Madelyn R. Ball, David H. K. Jackson, Joseph Paul Chada, Canan
Sener, Thomas F. Kuech, Rostam J. Madon, George W. Huber, and James A. Dumesic
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b01805 • Publication Date (Web): 06 Sep 2016
Downloaded from http://pubs.acs.org on September 9, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Page 1 of 49
ACS Catalysis
1
2
3
4
5
6
7
8
9
The Role of the Cu-ZrO2 interfacial sites for Ethanol Conversion to
Ethyl Acetate and Methanol Synthesis from CO2 and H2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Insoo Roa, Yifei Liua, Madelyn R. Balla, David H. K. Jacksona,b, Joseph Paul Chadaa, Canan
Senera,c, Thomas F. Kuecha,b, Rostam J. Madona, George W. Hubera, James A. Dumesica,c,*
a Department of Chemical and Biological Engineering, University of WisconsinꢀMadison, 1415
Engineering Drive, Madison, WI 53706, United States
b Materials Science Program, University of Wisconsin−Madison, 1509 University Avenue
Madison, WI 53706, United States
c Great Lakes Bioenergy Research Center, University of WisconsinꢀMadison, 1552 University
Ave., Madison, WI 53726, United States
Corresponding Author
*Prof. James A. Dumesic, Eꢀmail: jdumesic@wisc.edu
Keywords: Interfacial sites; Bimetallic catalyst; Active site; Control surface reactions (CSR);
Atomic layer deposition (ALD), Selective ethanol conversion to ethyl acetate; CO2
hydrogenation
Abstract
Wellꢀdefined Cu catalysts containing different amounts of zirconia were synthesized by
controlled surface reactions (CSR) and atomic layer deposition methods and studied for the
selective ethanol conversion to ethyl acetate and for methanol synthesis. Selective deposition of
ZrO2 on underꢀcoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced
by UVꢀVis absorption spectroscopy, scanning transmission electron microscopy, and inductively
coupled plasmaꢀabsorption emission spectroscopy. The concentrations of Cu and CuꢀZrO2
ACS Paragon Plus Environment

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
ACS Catalysis
Page 2 of 49
1
2
3
4
5
6
7
8
9
interfacial sites were quantified using a combination of subꢀambient CO Fourier transform
infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the
Cu and ZrO2 species for these catalysts were determined using Xꢀray absorption near edge
structure measurements, showing that these species were present primarily as Cu0 and Zr4+,
respectively. It was found that the formation of CuꢀZrO2 interfacial sites increased the turnover
frequency by an order of magnitude in both ethanol conversion to ethyl acetate and methanol
synthesis from CO2 and H2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1. Introduction
Copperꢀbased catalysts are used in a wide variety of reactions, such as methanol synthesis,
methanol steam reforming, water gas shift (WGS), and ethanol conversion. The conversion of
ethanol to ethyl acetate consists of a twoꢀstep process in which ethanol is first dehydrogenated to
acetaldehyde, which then undergoes coupling to form ethyl acetate. Previous studies have
investigated this reaction over copperꢀbased catalysts on different supports and shown that the
type of support used influences product selectivity.1 For example, the rate of formation of ethyl
acetate over Cu/ZrO2 and Cu/ZnO is an order of magnitude faster than over Cu/Al2O3 and
Cu/SiO2 catalysts.1a, b This enhanced reactivity for production of ethyl acetate over Cu/ZrO2 was
attributed to the higher rate of coupling occurring on the ZrO2 support in Cu/ZrO2 compared to
Cu sites in Cu/SiO2.1b In contrast, the presence of Cu0ꢀZrO2 interfacial sites was proposed to be
responsible for the higher rate of ethyl acetate formation over Cu/ZrO2 compared to Cu/SiO2 by
other studies.1c, d The same reaction was also studied over CuꢀZnꢀZrꢀAlꢀO catalysts, and it was
found that the coupling of ethanol and acetaldehyde occurs over mixed metalꢀoxide sites.2 In
ACS Paragon Plus Environment

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Page 3 of 49
ACS Catalysis
1
2
3
4
5
6
7
spite of a large volume of work, the nature of the active sites involved in selective ethanol
conversion to ethyl acetate reaction over supported copper catalysts remains elusive.
8
9
Compared to ethanol conversion reactions, there have been a larger number of studies to
understand the role of interfacial sites in methanol synthesis from synthesis gas (CO/CO2/H2). It
was reported that the active sites for methanol synthesis over Cu/ZnO/Al2O3 catalysts are located
at stepped (defective) Cu sites decorated with Zn atoms.3 Similar work demonstrated the
importance of CuꢀZnOx interfacial sites for methanol synthesis. It was found that the turnover
frequency (TOF) of methanol formation over a Cu (111) surface decorated with Zn at a coverage
of 19% (ꢀꢁꢂ = 0.19) is an order of magnitude higher than that over a clean Cu (111) singleꢀ
crystal surface.4 Interestingly, the promoting effect was only observed for Zn on Cu (111) but not
on Cu (110) and Cu (100) surfaces, suggesting that a stepped Cu surface decorated with Zn is the
active site for the methanol synthesis.4ꢀ5 Besides promotion caused by the interaction between Cu
and Zn, Bell and coꢀworkers demonstrated the promoting effect of ZrO2 on Cu/SiO2.6 The rate of
methanol formation over 30.5 wt% ZrO2 deposited on Cu/SiO2 is 25 times higher than the rate
over Cu/SiO2 for CO2 hydrogenation. Higher activity over the ZrO2ꢀpromoted Cu/SiO2 catalyst
was ascribed to the effective adsorption of CO2 on ZrO2 and enhanced methanol synthesis on the
ZrO2 surface with hydrogen supplied by spillover from Cu.7 In addition, it was concluded that
the ZrO2ꢀpromoted Cu/SiO2 catalyst behaves in a bifunctional manner.7c, 8 Wokaun and coꢀ
workers suggested the importance of interfacial sites between Cu and ZrO2 in the methanol
synthesis reaction from CO2/H2.9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The nature of the active Cu phase under reaction conditions for both ethanol conversion
to ethyl acetate and methanol synthesis is still a subject of controversy. Previous studies
ACS Paragon Plus Environment