5. Interface Control between Spinel Oxides and Ceria to Understand the Role of Ceria during
5.4. Conclusion
We synthesized spinel oxide NCs with controlled layers of CeO2 by a selective deposition protocol. Co3O4, Mn3O4, and Fe3O4 NCs with 1, 3, and 6 facets covered by CeO2 layers were prepared by controlling the surfactant concentration and pH. When CeO2 was deposited on Co3O4 and Mn3O4
NCs, the TOFs achieved for the CO oxidation reaction were higher than those of the pristine NCs due to the interfacial effect. Various in situ characterization techniques revealed that the attached CeO2
supplies oxygen to the Co3O4 surface, preventing it from being easily reduced under high-temperature reducing environments. The reduction of Ce4+ to Ce3+ and the subsequent charge transfer to Co3O4 were confirmed by NAP-XPS. The addition of CeO2 layers was found to provide sufficient oxygen to the Co3O4 surface, resulting in a high TOF, which clearly demonstrates that the CO oxidation process occurred via the MvK mechanism. The Co3O4 NCs completely covered by CeO2 (CoCe-6F) exhibited a lower TOF than that of CoCe-3F, demonstrating that the CO oxidation activity is directly related to the amount of the exposed Co3O4-CeO2 interface. The same trend was observed for H2 oxidation.
Moreover, the charge transfer accelerated by the Co3O4-CeO2 interface was also demonstrated by hot electron flow measurements during H2 oxidation using a catalytic nanodiode. These in-depth studies using well-defined oxide nanostructures combined with in situ characterization have therefore provided insights to establishing the origin of the activity enhancement and charge transfer at the interface.
5.5 References
1. Somorjai, G. A., Li, Y. Introduction of Surface Chemistry and Catalysis, 2nd Edition; Wiley-VCH:
New York, 2010.
2. van Deelen, T.W.; Hernández Mejía, C.; de Jong, K.P. Nat. Catal. 2019, 2, 955‒970.
3. Li, Z.; Ji, S. F.; Liu, Y. W.; Cao, X.; Tian, S. B.; Chen, Y. J.; Niu, Z. G.; Li, Y. D. Chem. Rev. 2020, 120, 623‒682.
4. Xie, C. L.; Niu, Z. Q.; Kim, D.; Li, M. F.; Yang, P. D. Chem. Rev. 2020, 120, 1184‒1249.
5. Campbell, C. T. Nat. Chem. 2012, 4, 597‒598.
6. Park, J. Y.; Baker, L. R.; Somorjai, G. A. Chem. Rev. 2015, 115, 2781‒2817.
7. Karim, W.; Spreafico, C.; Kleibert, A.; Gobrecht, J.; VandeVondele, J.; Ekinci, Y.; van Bokhoven, J. A. Nature 2017, 541, 68‒71.
8. Rodriguez, J. A.; Ma, S.; Liu, P.; Hrbek, J.; Evans, J.; Perez, M. Science 2007, 318, 1757‒1760.
9. Cargnello, M.; Doan-Nguyen, V. V. T.; Gordon, T. R.; Diaz, R. E.; Stach, E. A.; Gorte, R. J.;
Fornasiero, P.; Murray, C. B. Science 2013, 341, 771‒773.
10. Yoon, S.; Oh, K.; Liu, F. D.; Seo, J. H.; Somorjai, G. A.; Lee, J. H.; An, K. ACS Catal. 2018, 8, 5391‒5398.
11. Montini, T.; Melchionna, M.; Monai, M.; Fornasiero, P. Chem. Rev. 2016, 116, 5987‒6041.
12. Kim, H. Y.; Lee, H. M.; Henkelman, G. J. Am. Chem. Soc. 2012, 134, 1560‒1570.
13. Beniya, A.; Higashi, S. Nat. Catal. 2019, 2, 590‒602.
14. Wu, C. H.; Liu, C.; Su, D.; Xin, H. L.; Fang, H. T.; Eren, B.; Zhang, S.; Murray, C. B.; Salmeron, M. B. Nat. Catal. 2019, 2, 78‒85.
15. Carrettin, S.; Concepcion, P.; Corma, A.; Nieto, J. M. L.; Puntes, V. F. Angew. Chem. Int. Edit.
2004, 43, 2538‒2540.
16. Guzman, J.; Carrettin, S.; Corma, A. J. Am. Chem. Soc. 2005, 127, 3286‒3287.
17. An, K.; Alayoglu, S.; Musselwhite, N.; Plamthottam, S.; Melaet, G.; Lindeman, A. E.; Somorjai, G. A. J. Am. Chem. Soc. 2013, 135, 16689‒16696.
18. Xie, X. W.; Li, Y.; Liu, Z. Q.; Haruta, M.; Shen, W. J. Nature 2009, 458, 746‒749.
19. Xu, J.; Deng, Y. Q.; Zhang, X. M.; Luo, Y.; Mao, W.; Yang, X. J.; Ouyang, L.; Tian, P. F.; Han, Y. F. ACS Catal. 2014, 4, 4106‒4115.
20. Lukashuk, L.; Yigit, N.; Rameshan, R.; Kolar, E.; Teschner, D.; Havecker, M.; Knop-Gericke, A.;
Schlogl, R.; Fottinger, K.; Rupprechter, G. ACS Catal. 2018, 8, 8630‒8641.
21. Jansson, J.; Palmqvist, A. E. C.; Fridell, E.; Skoglundh, M.; Osterlund, L.; Thormahlen, P.;
Langer, V. J. Catal. 2002, 211, 387‒397.
22. Wang, H. F.; Kavanagh, R.; Guo, Y. L.; Guo, Y.; Lu, G. Z.; Hu, P. J. Catal. 2012, 296, 110‒119.
23. Bae, J.; Shin, D.; Jeong, H.; Kim, B. S.; Han, J. W.; Lee, H. ACS Catal. 2019, 9, 10093‒10100.
24. Lukashuk, L.; Fottinger, K.; Kolar, E.; Rameshan, C.; Teschner, D.; Havecker, M.; Knop-Gericke, A.; Yigit, N.; Li, H.; McDermott, E.; Stoger-Pollach, M.; Rupprechter, G. J. Catal. 2016, 344, 1‒
15.
25. Lundgren, E.; Zhang, C.; Merte, L. R.; Shipilin, M.; Blomberg, S.; Hejral, U.; Zhou, J. F.;
Zetterberg, J.; Gustafson, J. Acc. Chem. Res. 2017, 50, 2326‒2333.
26. Voychok, D.; Guild, C. J.; Dissanayake, S.; Llorca, J.; Stavitski, E.; Liu, Z. Y.; Palomino, R. M.;
Waluyo, I.; Li, Y. Y.; Frenkel, A. I.; Rodriguez, J. A.; Suib, S. L.; Senanayake, S. D. J. Phys.
Chem. C 2018, 122, 8998‒9008.
27. Oh, M. H.; Cho, M. G.; Chung, D. Y.; Park, I.; Kwon, Y. P.; Ophus, C.; Kim, D.; Kim, M. G.;
Jeong, B.; Gu, X. W.; Jo, J.; Yoo, J. M.; Hong, J.; McMains, S.; Kang, K.; Sung, Y. E.; Alivisatos, A. P.; Hyeon, T. Nature 2020, 577, 359‒363.
28. Oh, M. H.; Yu, T.; Yu, S. H.; Lim, B.; Ko, K. T.; Willinger, M. G.; Seo, D. H.; Kim, B. H.; Cho, M. G.; Park, J. H.; Kang, K.; Sung, Y. E.; Pinna, N.; Hyeon, T. Science 2013, 340, 964‒968.
29. Guardia, P.; Di Corato, R.; Lartigue, L.; Wilhelm, C.; Espinosa, A.; Garcia-Hernandez, M.;
Gazeau, F.; Manna, L.; Pellegrino, T. ACS Nano 2012, 6, 3080‒3091.
30. Jia, H. L.; Du, A. X.; Zhang, H.; Yang, J. H.; Jiang, R. B.; Wang, J. F.; Zhang, C. Y. J. Am. Chem.
Soc. 2019, 141, 5083‒5086.
31. Banfield, J. F.; Welch, S. A.; Zhang, H. Z.; Ebert, T. T.; Penn, R. L. Science 2000, 289, 751‒754.
32. Zhu, G. X.; Yao, S. S.; Zha, H. L.; Liu, Z. M.; Li, Y. L.; Pan, H. H.; Tang, R. K. Langmuir 2016, 32, 8999‒9004.
33. Yang, S. W.; Gao, L. J. Am. Chem. Soc. 2006, 128, 9330‒9331.
34. Zhang, J. T.; Tang, Y.; Lee, K.; Min, O. Y. Science 2010, 327, 1634‒1638.
35. Pope, E. J. A.; Mackenzie, J. D. J. Non-Cryst. Solids 1986, 87, 185‒198.
36. Brinker, C. J.; Scherrer, G. W. Sol-Gel Science: The physics and Chemistry of Sol-Gel Process;
Academic Press, New York, 1990.
37. Jolivet, J. P. Metal Oxide Chemistry and Synthesis: From Solution to Solid State; Wiley, Chichester, U. K., 2000.
38. Yamada, Y.; Tsung, C. K.; Huang, W.; Huo, Z. Y.; Habas, S. E.; Soejima, T.; Aliaga, C. E.;
Somorjai, G. A.; Yang, P. D. Nat. Chem. 2011, 3, 372‒376.
39. Baker, L. R.; Kennedy, G.; Van Spronsen, M.; Hervier, A.; Cai, X. J.; Chen, S. Y.; Wang, L. W.;
Somorjai, G. A. J. Am. Chem. Soc. 2012, 134, 14208‒14216.
40. Ha, H.; An, H.; Yoo, M.; Lee, J.; Kim, H. Y. J. Phys. Chem. C 2017, 121, 26895‒26902.
41. Ha, H.; Yoon, S.; An, K.; Kim, H. Y. ACS Catal. 2018, 8, 11491‒11501.
42. Jampaiahab, D.; Velisojuc, V. K.; Devaiahd, D.; Singhb, M.; Mayese, E. L. M.; Coylea, V. E.;
Reddyc, B. M.; Bansalb, V.; Bhargava, S. K. Appl. Surf. Sci. 2019, 473, 209‒221.
43. Lee, Y.; He, G. H.; Akey, A. J.; Si, R.; Flytzani-Stephanopoulos, M.; Herman, I. P. J. Am. Chem.
Soc. 2011, 133, 12952‒12955.
44. Chen, X.; Mao, S. S. Chem. Rev. 2007, 107, 2891‒2959.
45. Park, J. Y.; Kim, S. M.; Lee, H.; Nedrygailov, I. I. Acc. Chem. Res. 2015, 48, 2475‒2483.
46. Lee, H.; Nedrygailov, I. I.; Lee, C.; Somorjai, G. A.; Park, J. Y. Angew. Chem. Int. Edit. 2015, 54, 2340‒2344.
47. Lee, H.; Lim, J.; Lee, C.; Back, S.; An, K.; Shin, J. W.; Ryoo, R.; Jung, Y.; Park, J. Y. Nat.
Commun. 2018, 9, 1‒8.
48. Ravel, B.; Newville, M. J. Synchrotron Radiat. 2005, 12, 537‒541.
Chapter 6
Summary and Suggestions for Future Works
6.1. Summary
This dissertation presents the rational design and the fundamental understanding of the CeO2- based nanomaterials for heterogeneous catalysis.
In a supported catalyst system, the metal-support interaction (MSI) between metal nanoparticles (NPs) and a specific supporting oxide is a key factor controlling catalytic activity and selectivity.
Therefore, various synthetic approaches such as particle size control and support morphology modulation have been introduced to the MSI. In particular, the MSI is prominent in highly reducing oxides that provide an additional oxygen source by having a reversible oxidation state. Among the reducible oxides, ceria (CeO2) has excellent oxygen storage capacity, which is reduced from Ce4+ to Ce3+ to produce lattice oxygen that participates in the reaction pathway. Owing to its superior characteristics, ceria has been widely used in many catalytic applications, for example, three-way catalysts (TWCs), reforming catalysts, and removal catalysts for the volatile organic compounds.
As one of the tuning strategies, we controlled the shape of the ceria into two different shapes: a cube ({100} plane) and an octahedron ({111} plane). Uniform Au NPs of 3 nm size were supported on each ceria surface, and catalytic CO oxidation was performed as a model reaction. The gold-ceria is a good model system due to the inactive catalytic property of the gold at the inert support materials. As a result, Au/CeO2-cubes had 4 times higher conversion frequency for CO oxidation compared to Au/CeO2-octahedra. In addition, the estimated reducibility and charge transfer at the gold-ceria interface were magnified at Au/CeO2-cubes. Furthermore, DFT calculation revealed that the additional activation barrier is required to form the O‒C‒O intermediate in Au/CeO2(111). This indicates that the CO oxidation pathway which follows the Mars van Krevelen mechanism strongly depends on the facet of ceria support.
However, in typical noble metal catalysts such as Pt, the reaction to the surface of metal NPs should be considered. In Pt/CeO2 system, CO oxidation reaction can follow the surface reaction pathway (Langmuir-Hinshelwood mechanism) and the interface reaction pathway (Mars van Krevelen mechanism). The comprehensive reaction mechanism is significantly affected by the catalyst structure that of particle sizes and support shapes. Thus, we prepared various sizes of Pt NPs (1, 2, and 3 nm) onto the ceria cube and octahedron. Uniform The CO oxidation was conducted to estimate the particle size-dependent support effect. In any size of Pt NPs, Pt/CeO2-cubes showed better catalytic activity for
CO oxidation. Interestingly, the support effect is maximized in 1 nm Pt and gradually decreased by increasing the particle size. DFT calculation with two Pt models (Pt9 NP and Pt56 rod) on the ceria slabs explained the influence of the particle size on the interfacial support morphology effect by oxygen vacancy formation energies. Consequently, the particle size and the support morphology are deeply related in the manner of MSI, thus they need joint consideration for the rational design of supported catalysts.
Transition metal doping is another representative method for catalyst design. We have introduced Cu doping and ceria morphology control together to investigate the combined effect of doping and support morphology. Copper was doped into two ceria of cube and octahedron and Pd was used as an active metal for the catalysts. Subsequently, the water-gas shift reaction, which generates hydrogen, was performed to evaluate the designed catalysts. The reaction results showed that the turnover frequency for the water-gas shift reaction (WGSR) was higher in the CeO2 cube, regardless of the presence of the copper dopant. Surprisingly, there was a synergistic effect of Cu doping and ceria morphology that the doping effect was magnified in the CeO2 cube. We discovered the origination of the synergy effect for two reasons. Firstly, Pd dispersion is strongly influenced by the facet of ceria. Experimental analyses (EXAFS and DRIFTS) and DFT calculations proved the different dispersion of Pd species: PdO single sites in CeO2(100) and PdO clusters in CeO2(111). Secondly, Cu dopant distribution is also significantly affected by the shape of the ceria. ToF-SIMS and DFT calculations indicated that Cu dopant favors locating on the surface of ceria more in CeO2(100). The combinational effects lead to the enhanced catalytic reactivity for the WGSR in the Cu-doped ceria cubes.
Spinel oxides (Co3O4, Mn3O4, and Fe3O4) are attracting attention as a promising catalytic material to replace the precious metal catalysts because it has several oxidation states at the same time and is reversible. In addition, the improved catalytic activity can be obtained by adding ceria to spinel oxides.
However, it was difficult to understand the interface of the composite oxide due to its complex structure.
We controlled the number of spinel oxide-ceria interface in colloidal NPs by regulating the growth of ceria. The ceria covered the surfaces of spinel oxides of 1, 3, and 6 sides, respectively, to control the number of interfaces exposed on the surface. Spinel oxide NPs sequentially covered with ceria were used as a model catalyst (CO oxidation reaction) for oxide interface studies. We have found that ceria prevents the reduction of cobalt oxide through several in situ analysis characterizations. In addition, NAP-XPS analysis and hot electron detection showed that charge transfer at the Co3O4-CeO2 interface is the origin of high catalytic performance. These results directly demonstrate the role of ceria in complex oxide catalysts.
6.2. Suggestions for Future Works
In this dissertation, several future works are proposed to expand the scope of ceria catalyst
application and to utilize the well-defined structure of other oxide nanocrystals (NCs). In this dissertation, relatively simple catalytic reactions such as CO oxidation and WGSR were tested using ceria NCs as a catalyst material. Further, if ceria nanocatalyst is applied to more advanced catalytic reactions, it is possible to propose a catalyst structure that can be helpful in the actual industry. The production of plastic reached 368 million tons as of 2019, showing a continuous increase, however, only 14% of total plastic is recycled and the rest is disposed of through landfill or incineration. Among plastics, polyethylene (PE) is used in plastic bags and packaging containers and is a representative material that accounts for the largest share (29%) of plastic production. Recently, Ru-based catalysts have been reported for PE hydrogenolysis.1 Ru is considered a useful catalytic material for hydrogenolysis because it cleaves hydrogen well. Notably, Ru/CeO2 has been reported as an effective catalyst for PE hydrogenolysis2 and a difference in the activity of the CO oxidation reaction according to each CeO2 shape has been studied.3 Therefore, it is expected that a difference in reactivity depending on the shape of CeO2 in Ru/CeO2 catalysts can be observed in PE hydrogenolysis reaction. Consequently, ceria is very important in changing the properties of the catalyst to increase activity and selectivity, thus it is necessary to focus research on the catalyst development using ceria in the new field.
In addition to ceria, metal oxides with well-defined structures can be used as model catalysts for catalytic reactions. Copper oxide (Cu2O) can be applied in a variety of catalytic applications due to its low cost, non-toxicity and unique electrical properties. The Cu2O (100), (110), and (111) surfaces are the ones most commonly investigated due to their different polarity, symmetry, and oxygen supply ability.4 Typically, Cu2O cube and octahedron NCs can be obtained by controlling the PVP (polyvinylpyrrolidone) concentration in the colloidal synthesis method. Zhang et al. found that the activity of the WGSR in Cu2O(100) is significantly better than that of Cu2O(111).5 Besides, when CeO2
is added to Cu2O, the activity can be expected to increase through the role of oxygen buffer in the WGSR redox mechanism.6 By borrowing the concept studied by combining the doping and morphology control of previous studies, we intend to manufacture a nanocatalyst by doping Ce in Cu2O whose shape is controlled. The Cu2O facet-dependent Ce doping effect would be expected by applying the corresponding NCs into the WGSR.
6.3. References
1. Rorrer, J. E.; Beckham, G. T.; Román-Leshkov, Y. JACS Au 2021, 1, 8‒12.
2. Nakaji, Y.; Tamura, M.; Miyaoka, S.; Kumagai, S.; Tanji, M.; Nakagawa, Y.; Yoshioka, T.;
Tomishige, K. Appl. Catal. B 2021, 285, 119805.
3. Li, J. H.; Liu, Z. Q.; Cullen, D. A.; Hu, W. H.; Huang, J. E.; Yao, L. B.; Peng, Z. M.; Liao, P. L.;
Wang, R. G. ACS Catal. 2019, 9, 11088‒11103.
4. Zhao, X.; Susman, M. D.; Rimer, J. D.; Bollini, P. ChemCatChem 2021, 13, 6‒27.
5. Zhang, Z. H.; Wang, S. S.; Song, R.; Cao, T.; Luo, L. F.; Chen, X. Y.; Gao, Y. X.; Lu, J. Q.; Li, W. X.; Huang, W. X. Nat.Commun. 2017, 8, 488.
6. Barrio, L.; Estrella, M.; Zhou, G.; Wen, W.; Hanson, J. C.; Hungria, A. B.; Hornes, A.;
Fernandez-Garcia, M.; Martinez-Arias, A.; Rodriguez, J. A. J. Phys. Chem. C 2010, 114, 3580‒ 3587.
Nomenclature
DRIFTS Diffuse reflectance infrared fourier transform spectroscopy DFT Density functional theory
DI Deionized
DRM Dry reforming reaction of methane EDS Energy dispersive spectroscopy EELS Electron energy loss spectroscopy EXAFS X-ray absorption fine structure
fcc Face-centered-cubic
FFT Fast fourier transform FWHM Full-width half maximum
GA Genetic algorithm
GC Gas chromatography
HAADF-STEM High-angle annular dark-field scanning transmission electron microscopy hcp Hexagonal closed packed
HRTEM High-resolution transmission electron microscopy
ICP-OES Inductively coupled plasma optical emission spectroscopy
IR Infrared
L-H Langmuir-Hinshelwood
MSI Metal-support interaction
MvK Mars van Krevelen
NAP-XPS Near ambient presuure X-ray photoelectron spectroscopy
NCs Nanocrystals
NPs Nanoparticles
OSC Oxygen storage capacity PAW Projector-augmented-wave
PBE Perdew–Burke–Ernzerhof
RT Room temperature
SEM Scanning electron microscopy
STEM Scanning transmission electron microscopy TCD Thermal conductivity detector
TEM Transmission electron microscopy TGA Thermogravimetric analysis
TOF Turnover frequency
ToF-SIMS Time-of-flight secondary ion mass spectroscopy
TON Turnover number
TPR Temperature-programmed reduction
TWCs Three way catalysts
UV Ultraviolet
VASP Vienna ab initio software package VOCs Volatile organic compounds WGSR Water-gas shift reaction WHSV Weight hourly space velocity
XANES X-ray absorption near-edge spectroscopy XAS X-ray absorption spectroscopy
XPS X-ray photoelectron spectroscopy
XRD X-ray diffraction
Acknowledgements
지난 6년여간의 학위 과정은 저 혼자만의 노력으로 이루어 낸 것이 아니라 많은 분들의 진실어린 조언과 도움, 그리고 믿음을 통해 헤쳐나갈 수 있었습니다. 먼저, 연구를 대하는 자세와 많은 가르침을 통해 항상 제자들의 본보기가 되시는 지도교수님이신 안광진 교수님께 깊은 감사를 드립니다. 교수님의 첫 제자로 학위를 받을 수 있어 영광이었고, 교수님께서 주신 가르침과 격려는 부족한 제가 성장할 수 있는 발판이 되었습니다.
바쁘신 와중에도 저의 심사를 맡아주시고 귀한 조언을 아끼지 않으신 UNIST 주상훈, 장지욱, 권영국 교수님과 충남대학교 김현유 교수님께 큰 감사를 드립니다. 연구방향의 선정과 완성도를 높이는데에 많은 도움이 되었습니다. 또한 공동 연구를 통해 실험적, 이론적으로 제가 수행하기 힘든 부분을 도와주신 여러 교수님들께 감사의 말씀을 드립니다. 우선 나노입자 합성에 도움을 주신 서울대학교 현택환 교수님과 조진웅 학생, 이론적 계산을 도와주신 충남대학교 김현유 교수님과 하현우 박사님, 촉매 분석과 계산을 수행해주신 POSTECH 한정우 교수님과 장명곤 학생, 그리고 물질합성에 도움을 주신 UNIST 조승호 교수님과 장원식 학생께 논문 작성과 연구에 많은 도움을 주셔서 정말 감사드립니다. 또한 핫전자 검출을 도와주신 KAIST 박정영 교수님, TEM분석을 해주 신 UNIST 정후영 교수님, 가속기 분석에 도움을 주신 UNIST 신태주 교수님, XPS 분석을 밤낮 으로 도와주신 KBSI 정범균 박사님께도 감사의 말씀을 드립니다.
학위 과정 동안 연구 내외적으로 서로 많이 공감하며 추억을 함께 쌓은 우리 안랩 구성원들에게도 고맙다는 말을 전합니다. 연구실 초기 멤버로 고생도 많이 했지만 가장 오랜 시간을 함께한 의섭, 준경, 지현, 호정에게 진심으로 고맙습니다. 그리고 앞으로 우리 연구실의 중추 역할을 수행할 부사수인 지훈이와 은정, 병관, 대원, 윤정, 언우, 주은에게도 감사의 인사를 전하고, 우리 연구실 멤버 모두에게 긴 대학원 생활의 끝에 성공이 기다리고 있을 것이라 믿습니다. 또한 104동 8층에서 함께 생활한 동료 연구자들에게도 감사의 말을 전합니다. 개인적으로도 친분을 많이 쌓은 주랩의 두산, 진우, 재형, 태정, 호영, 이랩의 민경, 광영, 그리고 촉매센터 채주희 선생님께도 감사드립니다.
연구외적으로 저의 삶을 지탱하게끔 도움을 많이 준 친구들에게도 감사의 말을 전합니다. 만나면 언제나 편안한 고등학교 친구들인 섭, 선일, 승원, 영욱, 용우, 대학교 동기들인 근욱, 민, 승욱, 성동, 에녹, 원경, 태영, 중학교 친구들인 성보, 인기에게도 감사를 전합니다. 길었던 학위 과정동안 친구들의 존재로 인해 위로도 받으며 기쁨을 얻을 수 있어 연구를 지속할 수 있었습니다.
마지막으로 가장 소중한 우리 가족에게 감사를 표합니다. 늦은 나이까지 아들을 지원해주시고 언제나 믿어주신 부모님과 동생 보영이에게 진심으로 감사드립니다. 항상 아들에게 귀감이되는 아버지와 아들의 모든 것들을 챙겨주시는 어머니, 항상 고맙고 사랑합니다.