Shape Effect Undermined by Surface Reconstruction: Ethanol Dehydrogenation over Shape-Controlled SrTiO3 Nanocrystals

Guo Shiou Foo; Zachary D. Hood; Zili Wu

doi:10.1021/acscatal.7b03341

Shape Effect Undermined by Surface Reconstruction: Ethanol Dehydrogenation over Shape-Controlled SrTiO₃ Nanocrystals

Guo Shiou Foo
, Zachary D. Hood
, Zili Wu

Surface Chemistry & Catalysis Group

Research output: Contribution to journal › Article › peer-review

68 Scopus citations

Abstract

To gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid-base pair reactivity of shape-controlled SrTiO₃ (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubes of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the C_α-H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH₃, 2,6-di-tert-butylpyridine, CO₂, and SO₂, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid-base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid-base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. The finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.

Original language	English
Pages (from-to)	555-565
Number of pages	11
Journal	ACS Catalysis
Volume	8
Issue number	1
DOIs	https://doi.org/10.1021/acscatal.7b03341
State	Published - Jan 5 2018

Funding

This research is sponsored by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Part of the work including XRD, SEM, FTIR spectroscopy, and kinetic measurements was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Z.D.H. gratefully acknowledges a graduate fellowship from the National Science Foundation under Grant No. DGE- 1650044 and the Georgia Tech-ORNL Fellowship. The authors thank Victor Fung (University of California Riverside) for providing figures of SrTiO3 (001) and (110) surfaces. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. This research is sponsored by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Part of the work including XRD, SEM, FTIR spectroscopy, and kinetic measurements was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Z.D.H. gratefully acknowledges a graduate fellowship from the National Science Foundation under Grant No. DGE-1650044 and the Georgia Tech-ORNL Fellowship. The authors thank Victor Fung (University of California Riverside) for providing figures of SrTiO3 (001) and (110) surfaces. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Keywords

(001) facet
(110) facet
dehydrogenation
ethanol
strontium titanate
surface termination

Access to Document

10.1021/acscatal.7b03341

Cite this

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title = "Shape Effect Undermined by Surface Reconstruction: Ethanol Dehydrogenation over Shape-Controlled SrTiO3 Nanocrystals",

abstract = "To gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid-base pair reactivity of shape-controlled SrTiO3 (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubes of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the Cα-H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH3, 2,6-di-tert-butylpyridine, CO2, and SO2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid-base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid-base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. The finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.",

keywords = "(001) facet, (110) facet, dehydrogenation, ethanol, strontium titanate, surface termination",

author = "Foo, \{Guo Shiou\} and Hood, \{Zachary D.\} and Zili Wu",

note = "Publisher Copyright: {\textcopyright} 2017 American Chemical Society.",

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doi = "10.1021/acscatal.7b03341",

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T1 - Shape Effect Undermined by Surface Reconstruction

T2 - Ethanol Dehydrogenation over Shape-Controlled SrTiO3 Nanocrystals

AU - Foo, Guo Shiou

AU - Hood, Zachary D.

AU - Wu, Zili

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Y1 - 2018/1/5

N2 - To gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid-base pair reactivity of shape-controlled SrTiO3 (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubes of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the Cα-H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH3, 2,6-di-tert-butylpyridine, CO2, and SO2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid-base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid-base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. The finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.

AB - To gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid-base pair reactivity of shape-controlled SrTiO3 (STO) nanocrystals for the dehydrogenation of ethanol. Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubes of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the Cα-H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH3, 2,6-di-tert-butylpyridine, CO2, and SO2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid-base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid-base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. The finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape-controlled complex oxides such as perovskites.

KW - (001) facet

KW - (110) facet

KW - dehydrogenation

KW - ethanol

KW - strontium titanate

KW - surface termination

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