Size Regulation of Platinum Nanoparticles by Using Confined Spaces

2 days ago - Decomposition of the Pt-containing precursor occurs within the confined space between the template and silica walls. This leads to ... No...
0 downloads 13 Views 2MB Size
Download PDF
Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

Size Regulation of Platinum Nanoparticles by Using Confined Spaces for the Low-Temperature Oxidation of Ethylene Yu Kou and Lin-Bing Sun* State Key Laboratory of Materials-Oriented Chemical Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, College of Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing 210009, China S Supporting Information *

ABSTRACT: Noble-metal nanoparticles have attracted great attention because of their excellent catalytic activity. However, the activity of noblemetal nanoparticles is severely dependent on the size of the metal nanoparticles. Therefore, regulation of the nanoparticle size is of great importance. Herein we report an efficient strategy for the first time to regulate the size of platinum (Pt) nanoparticles in a typical mesoporous silica SBA-15 by using the confined spaces. The Pt-containing precursor is introduced to the confined spaces between the template and silica walls in as-prepared SBA-15 by grinding. Subsequent calcination allows template removal and precursor conversion in one step and avoids repeated calcination in conventional modification processes. This leads to the formation of Pt nanoparticles with smaller size, making Pt metal catalysts highly active. Hence, the catalytic activity of the oxidation of trace ethylene is very superior to that of those prepared by the conventional method. For a typical material, PtAS-5, containing 5.0 wt % Pt, the complete conversion of ethylene was achieved at 40 °C, which is lower than that on the catalyst PtCS-5 prepared by the conventional method (50 °C) as well as that on a series of catalysts reported previously.

■

INTRODUCTION Ethylene, a low-molecular-weight gaseous volatile organic compound, is an important industrial chemical; meanwhile, it has some negative effects such as photochemical pollution.1 Therefore, eliminating ethylene gas from some environments is of great necessity. For example, the removal of ethylene can decelerate the maturation of fruits and vegetables and keep them fresh for longer time. By using catalytic oxidation technology, the trace ethylene can be transformed completely to carbon dioxide and water. Until now, a collection of catalysts were attempted for the oxidation of ethylene, such as Au/ Co3O42 and copper manganese oxides.3 However, most of those catalysts show relatively low catalytic activities for the oxidation of ethylene, and the temperature for the complete conversion of ethylene is usually higher than 100 °C. For example, the temperature for 100% conversion of ethylene over the catalyst MCS/Co-30 is 185 °C,4 and the catalyst Au/Co3O4 can convert ethylene completely at 150 °C.2 Despite great efforts, the catalytic conversion of ethylene at low temperatures remains a great challenge. Noble metals have attracted wide interest as catalysts in the past few years because of their superior activity.5 Compared with pure noble-metal films, noble-metal nanoparticles are extensively studied.6,7 It is worth noting that the size of noblemetal nanoparticles can largely influence the catalytic activity.8 Among many noble metals, platinum (Pt) is widely used in catalysis, which has superior activity in some kinds of reactions, © XXXX American Chemical Society

such as oxidation and hydrogenation. Researchers have reported the use of Pt as active sites to catalyze the oxidation of hydrocarbons.9,10 Until now, some researchers have studied the catalytic performance and catalytic mechanism of Pt metal catalysts for the oxidation of ethylene. Ethylene reacts with oxygen to generate formaldehyde, which adsorbed on Pt. Then formaldehyde decomposes into carbon monoxide and hydrogen species, and these two intermediate species react with oxygen to generate the final products carbon dioxide and water.11 It has been discovered that the size of Pt nanoparticles (Pt NPs) has a direct impact on the activity of Pt catalysts, while it is not easy to fabricate Pt NPs with smaller size. Mesoporous silica, a kind of material with high surface area and large pore volume, is an ideal support to regulate the size of metal nanoparticles. Many attempts have been made to produce a small size of metal nanoparticles on mesoporous silica by various methods including ion implantation,12 sol−gel processing,13 and sputtering. Functional groups (e.g., NH2,14 SH,15 and SO3H16) are usually grafted onto mesoporous silica to promote regulation of the size of metal nanoparticles. This traditional method is useful; however, the complicated surface functionalization is tedious. Meanwhile, this traditional method usually ignored the nature of as-prepared mesoporous silica.17,18 Actually, between the template and silica walls in Received: November 29, 2017

A

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry as-prepared mesoporous silica, there is a special microenvironment, which can provide confined spaces and abundant silanol groups; these are beneficial to promoting the size regulation of noble-metal nanoparticles. Hence, the fabrication of a small size of noble-metal nanoparticles and high-activity metal catalysts by using the confined space is extremely desirable. Here, we report an efficient strategy to regulate the size of Pt NPs by using confined spaces. The Pt-containing precursor is introduced to the confined spaces between the template and silica walls in as-prepared SBA-15 (denoted as AS) by grinding. Decomposition of the Pt-containing precursor occurs within the confined spaces between the template and silica walls (Scheme 1). During calcination, the size of Pt NPs can be well Scheme 1. Formation of (A) Small-Size Pt NPs in Confined Spaces and (B) Large-Size Pt NPs in Conventional Mesoporous Silica

Figure 1. (A) Low-angle XRD patterns, (B) wide-angle XRD patterns, (C) N2 adsorption−desorption isotherms, and (D) pore-size distributions of CS, PtAS-5, and PtCS-5. Curves are plotted offset for clarity.

Compared with the PtCS, the PtAS samples exhibit relatively broader diffraction peaks of metallic Pt, which suggest smaller size Pt NPs in the PtAS samples.25 According to the Scherrer equation, the size of the Pt NPs was calculated by use of the Pt(111) diffraction peak. The size of the Pt NPs in PtAS-5 is 3.0 nm, which is obviously smaller than that in PtCS-5 (13.1 nm; Table 1). What is more, the size of the Pt NPs in all of the PtAS samples is smaller compared with that of the PtCS samples. According to the above results, it is reasonable to say that using the AS as the support is obviously beneficial for the formation of small-size Pt NPs. The surface components of Pt NPs are measured by X-ray photoeectron microscopy (XPS). It is apparently seen from Figures 2 and S3 that both the PtAS and PtCS samples show double peaks of zero-valence Pt 4f7/2 and 4f5/2 centered at 74.2 and 71.0 eV, which correspond to metallic Pt NPs.26 This result indicates that there is no existence of other valence Pt ions (such as Pt4+ and Pt2+) but only the metallic Pt in the samples. Meanwhile, this also indicates that PtO could be reduced absolutely to metallic Pt by calcination at 200 °C under a H2 atmosphere. The N2 adsorption−desorption isotherms of all samples are shown in Figures 1C and S4. This reflects that the samples are all of type IV isotherms with an H1-type hysteresis loop, which is the same as CS and is attributed to the characteristics of materials with regular mesoporous structure.21 Compared with the PtAS samples, the PtCS samples show a “tail” during the desorption stage, which becomes clear gradually with an increase of the Pt loading. Compared to the samples with the same noble-metal content, the hysteresis loop of PtCS moves to the area of lower relative pressure. These results illustrate that Pt NPs prepared using the confined spaces have small size. Further calculation shows that the samples with the same noble-metal content, all samples prepared by our strategy, have higher surface areas and pore volumes, in line with the sample using the conventional method (Table 1), which provides evidence for the small size of Pt NPs in the pores of the

controlled by the confined effect. It is simple and easy for our strategy, which allows template removal and precursor conversion in one step and avoids repeated calcination in a conventional modification process. It can not only save time but also reduce energy consumption.19 The results show that noble-metal Pt NPs prepared by our strategy have smaller size than that using the conventional method.20 The size of Pt NPs in PtAS-1 (1.0 wt %) prepared by our strategy is only 0.5 nm. Also, the typical material PtAS-5 containing 5.0 wt % Pt has a size of 3.0 nm. The size of Pt NPs in PtAS-5 is much smaller than that in the sample PtCS-5 prepared by the conventional method (13.2 nm). Meanwhile, the Pt NPs supported on SBA15 prepared by our strategy showed higher activity in the catalytic oxidation of ethylene.

■

RESULTS AND DISCUSSION Structural and Surface Properties. Characterization of the samples was carried out by different physicochemical methods. The low-angle X-ray diffraction (XRD) patterns (Figures 1A and S1) show that the Pt-containing samples have a strong diffraction peak and two weak ones, which is similar to the support CS; this could correspond to (100), (110), and (200) reflections and is attributed to a two-dimensional hexagonal pore symmetry.21,22 Figure 1A reflects that the samples PtAS-5 and PtCS-5 retain the ordered mesoporous structure after the loading of Pt NPs. Compared with the support CS, the Pt-containing samples possess an obviously weaker intensity of the diffraction peaks, which can be attributed to the decrease of the scatter contrast between the pore volume and pore space after the introduction of Pt NPs. All of the samples show a broad diffraction peak centered at 23° in the wide-angle XRD patterns, which corresponds to amorphous silica walls (Figures 1B and S2).23 Pt-containing samples have three characteristic XRD peaks at 40°, 46°, and 67° derived from metallic Pt NPs (JCPDS 04-0802).24 B

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Physicochemical Properties and Catalytic Performance of CS and Modified Samples

a

sample

SBET (m2·g−1)

Vp (cm3·g−1)

Dp (nm)

CS PtAS-1 PtAS-3 PtAS-5 PtCS-1 PtCS-3 PtCS-5

905 779 742 721 748 722 504

1.147 1.062 1.038 1.006 0.904 0.856 0.572

8.0 8.0 7.9 7.6 8.0 7.8 7.4

dPta (nm)

conversion at 25 °C (%)

temperature for 100% conversion (°C)

0.5 2.1 3.0 1.2 5.4 13.1

0 38.6 39.0 52.0 22.3 19.1 30.8

66.8 52.0 39.9 82.1 58.7 49.9

Estimated from XRD using the Scherrer equation.

Figure 2. XPS peak fitting of Pt 4f7/2 and 4f5/2 spectra of (A) PtAS-5 and (B) PtCS-5.

support. Furthermore, it is reasonable to believe that the large size of Pt NPs and the use of CS change the shape of the adsorption−desorption isotherm and the physicochemical properties for PtCS. It is of great importance to characterize the structure of the support SBA-15 and the size of Pt NPs by transmission electron microscopy (TEM). For both PtAS and PtCS, the periodic mesopores with uniform pore size and wall thickness are obviously seen from the bright−dark TEM images (Figure 3),27 which shows that the ordered pore structure of the supports is not destroyed after the introduction of Pt NPs. The bright-field TEM images also provide powerful evidence of the presence of Pt NPs on the supports. It can be observed from the bright-field image that the size of the Pt NPs in the PtAS-5 sample is smaller and loaded uniformly. In contrast, the bright-field image of PtCS-5 shows some large size of the Pt NPs. The dark-field images of PtAS-5 and PtCS-5 further proved the smaller Pt NPs in PtAS-5 than in PtCS-5. The average size of the Pt NPs in PtAS-5 is 2.8 nm by further analysis of the TEM image. However, the size of Pt in the sample PtCS-5 is 13.2 nm. These results fit well with the wide-angle XRD patterns. The size of the Pt NPs in PtAS is smaller than that in PtCS. According to the above analysis results, it is safe to say that the use of the asprepared SBA-15 existing confined space could decrease the size of the Pt NPs to a great extent. Catalytic Performance on Ethylene Oxidation. An ethylene concentration of 0.32 vol % in the initial gas was used to research the activity of Pt catalysts in this work. Figures 4A and S5 and S6 show the curves of ethylene conversion over different samples. Complete oxidation of trace ethylene was measured on samples PtAS and PtCS over a wide range of reaction temperatures (25−150 °C). The conversion of ethylene over pure mesoporous silica CS was extremely low, which suggests that the oxidation of ethylene cannot proceed at all in the absence of Pt NPs. After the introduction of Pt NPs into the support, the catalytic activities of PtAS and PtCS were obviously improved. Meanwhile, the catalytic activity of PtAS was obviously superior to that of PtCS, which can give evidence that the preparation method using the template-occluded AS

Figure 3. Bright-field TEM images of (A) PtAS-5 and (B) PtCS-5. Dark-field TEM images of (C) PtAS-5 and (D) PtCS-5. Corresponding particle-size distributions of (E) PtAS-5 and (F) PtCS-5.

Figure 4. (A) Conversion profiles for ethylene oxidation over different samples and (B) reaction tests at 40 °C for ethylene oxidation with time-on-stream over PtAS-5.

has a significant influence on the catalytic performance. Table 1 also shows the catalytic conversion of trace ethylene over PtAS C

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

conducted at 40 °C even as the reaction time is increased to 150 h. To study the deactivation behavior of catalysts, a high reaction temperature of 90 °C was employed. As shown in Figure S8, the conversion of ethylene over PtAS-5 at 90 °C is 100% for more than 24 h. With an increase of the reaction time, the catalytic activity of PtAS-5 decreases gradually. The catalyst PtAS-5 shows no activity upon the oxidation of ethylene when the reaction time exceeds 34 h. The wide-angle XRD pattern of PtAS-5 after deactivation was measured (Figure S9). It is obvious that the Pt NPs in PtAS-5 seriously aggregated. In short, the present catalysts show high stability upon ethylene oxidation at a low temperature of 40 °C, which is promising for applications in storehouse storage. Proposed Mechanism. On the basis of the aforementioned results, it is safe to say that noble-metal Pt NPs can be introduced to the support with a small size by using our method and the samples show better catalytic activity than those prepared using the conventional method. It is reasonable to believe that the confined space between the template and silica walls is of great importance in regulation of the size of noble-metal nanoparticles. As shown in Figure 7, the weight

and PtCS. The catalyst PtAS-1 containing 1.0 wt % Pt exhibits a conversion of 38.6% at 25 °C and such a catalytic activity is higher than that of PtCS-1 (22.3%) possessing the same Pt content prepared by the conventional method. PtAS-1 can catalyze the conversion of ethylene completely at 66.8 °C, while that over PtCS-1 requires a higher reaction temperature of 82.0 °C. With an increase of the loading of Pt, the activity of the catalysts increases. For PtAS-3, the ethylene conversion reaches 39.0% at 25 °C, and the temperature for complete oxidation is 52.0 °C. In contrast to the catalytic performance of PtCS-3, the sample PtAS-3 shows a lower temperature for complete oxidation and higher catalytic activity. When the loading of Pt is enhanced to 5.0 wt %, the catalytic activity of the sample is further improved. Typically, the ethylene conversion is as high as 52.0% at 25 °C by using PtAS-5 as the catalyst, which is higher than that over PtCS-5 (30.8%) and other Pt-containing samples under the same reaction conditions. What is more, the conversion of ethylene over PtAS-5 remains approximately 100% at a pretty low temperature of 40 °C. Among these samples, there is no doubt that PtAS-5 has the best catalytic activity for the oxidation of ethylene. In contrast to some reported catalysts in the literature, the catalytic activity of the sample PtAS-5 is better (Table S1). No particle size change was observed for the spent catalyst from wide-angle XRD patterns (Figures 5 and S7). Meanwhile, the recyclability of the catalyst

Figure 7. (A) TGA and (B) differential thermal gravimetry curves of AS, PtAS-5, and PtCS-5. Figure 5. Wide-angle XRD patterns of PtAS-5 (a) before and (b) after reaction at 40 °C.

loss of the sample AS is 55% after reaching 600 °C, and the decomposition temperature of the template P123 in the support AS is about 170 °C, which is obviously lower than that of pure P123 (210 °C).28 This is because silica walls can promote decomposition of the block copolymer. Meanwhile, it is worth noting that decomposition of the template occurs at 188 °C in the sample PtAS-5, which is also higher than the decomposition temperature of P123 in AS. The decomposition temperature of the template in other Pt-containing samples is also higher than that in the support AS (Figure S10). This result indicates that the noble-metal precursor has been introduced to the confined spaces successfully. Therefore, the silica walls cannot act as catalysts in decomposition of the template because of separation of the silica walls and template. As a result, the confined spaces constructed between the template and silica walls in mesoporous silica provide a desired platform for the fabrication of noble-metal nanoparticles. Besides the confined-space effect, the rich silanol groups (Si− OH) existing in the support AS could also be beneficial to controlling the size of the nanoparticles. The IR spectra of the supports and Pt-containing samples before and after calcination are shown in Figures 8 and S11 and S12. The support AS shows IR bands in the range 2850−3000 cm−1, which can be attributed to the bending vibrations of P123. It is worth noting that the IR band appeared at 960 cm−1, which is caused by the

was examined (Figure 6). The sample PtAS-5 can still convert ethylene completely after running for five cycles, which suggests better recyclability of the catalyst. The durability of Pt-containing catalysts was investigated. As shown in Figure 4B, the catalytic conversion of ethylene over PtAS-5 at 40 °C remains at approximately 100% for more than 12 h. Moreover, no loss in activity is observed for the reaction

Figure 6. Recyclability of PtAS-5 as the catalyst for the oxidation of ethylene at 40 °C.. D

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 8. IR spectra of SBA-15, PtAS-5, and PtCS-5 (A) before and (B) after calcination.

ORCID

stretching vibration of silanol groups. It is clear that the PtAS samples had more silanol groups than PtCS before calcination. During calcination, the silanol groups on the silica walls can interact with metal nanoparticles, which benefits the preparation of small-size Pt NPs. Therefore, a higher hydroxyl density can promote regulation of the size of noble-metal nanoparticles when metal nanoparticles are introduced to the support.29

Lin-Bing Sun: 0000-0002-6395-312X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21722606 and 21576137) and the Project of Priority Academic Program Development of Jiangsu Higher Education Institutions.

■

CONCLUSIONS In summary, a facile, efficient strategy has been developed to regulate the noble-metal nanoparticles in confined spaces. A smaller size of noble-metal Pt NPs was achieved by using asprepared mesoporous silica AS; in contrast, large-size Pt NPs produce conventional calcined mesoporous silica CS. The small size of the metal nanoparticles is attributed to the confined spaces between the template and silica walls in the support AS and the strong interaction with the support because of the abundant silanol groups on the silica walls of AS. Meanwhile, in comparison with the samples by the conventional method, the samples prepared by our strategy exhibit better catalytic activity of ethylene oxidation. What is more, the catalytic activity of the sample PtAS-5 is obviously superior to that of some samples reported in the literature. On the one hand, the strategy of confined space might provide a new way to regulate the size of metal nanoparticles with small size, which should enable one to incorporate metals, bimetals, and even composites into mesoporous silica to prepare new functional materials. On the other hand, it is meaningful to further decrease the size of the Pt NPs on the basis of our work. In addition to the use of confined spaces, work is in progress to enhance the interaction between metal nanoparticles and the surface of supports via surface modification (e.g., doping heteroatoms). As a result, catalysts with even smaller size of metal nanoparticles, which are highly expected in various applications, are supposed to be prepared.

■

■

(1) Ma, C. Y.; Mu, Z.; Li, J. J.; Jin, Y. G.; Cheng, J.; Lu, G. Q.; Hao, Z. P.; Qiao, S. Z. Mesoporous Co3O4 and Au/Co3O4 Catalysts for LowTemperature Oxidation of Trace Ethylene. J. Am. Chem. Soc. 2010, 132, 2608−2613. (2) Li, J. J.; Ma, C. Y.; Xu, X. Y.; Yu, J. J.; Hao, Z. P.; Qiao, S. Z. Efficient Elimination of Trace Ethylene over Nano-Gold Catalyst under Ambient Conditions. Environ. Sci. Technol. 2008, 42, 8947− 8951. (3) Njagi, E. C.; Genuino, H. C.; King’ondu, C. K.; Dharmarathna, S.; Suib, S. L. Catalytic Oxidation of Ethylene at Low Temperatures Using Porous Copper Manganese Oxides. Appl. Catal., A 2012, 421422, 154−160. (4) Li, W. C.; Zhang, Z. X.; Wang, J. T.; Qiao, W. M.; Long, D. H.; Ling, L. C. Low Temperature Catalytic Combustion of Ethylene over Cobalt Oxide Supported Mesoporous Carbon Spheres. Chem. Eng. J. 2016, 293, 243−251. (5) Corma, A.; Garcia, H. Supported Gold Nanoparticles as Catalysts for Organic Reactions. Chem. Soc. Rev. 2008, 37, 2096−2126. (6) Dole, H. A. E.; Costa, A. C. G. S. A.; Couillard, M.; Baranova, E. A. Quantifying Metal Support Interaction in Ceria-Supported Pt, PtSn and Ru Nanoparticles Using Electrochemical Technique. J. Catal. 2016, 333, 40−50. (7) Crampton, A. S.; Roetzer, M. D.; Schweinberger, F. F.; Yoon, B.; Landman, U.; Heiz, U. Ethylene Hydrogenation on Supported Ni, Pd and Pt Nanoparticles: Catalyst Activity, Deactivation and the D-Band Model. J. Catal. 2016, 333, 51−58. (8) Zhu, Q.; Tsumori, N.; Xu, Q. Immobilizing Extremely Catalytically Active Palladium Nanoparticles to Carbon Nanospheres: A Weakly-Capping Growth Approach. J. Am. Chem. Soc. 2015, 137, 11743−11748. (9) Yashnik, S. A.; Denisov, S. P.; Danchenko, N. M.; Ismagilov, Z. R. Synergetic Effect of Pd Addition on Catalytic Behavior of Monolithic Platinum-Manganese-Alumina Catalysts for Diesel Vehicle Emission Control. Appl. Catal., B 2016, 185, 322−336. (10) Mironov, O. A.; Bischof, S. M.; Konnick, M. M.; Hashiguchi, B. G.; Ziatdinov, V. R.; Goddard, W. A.; Ahlquist, M.; Periana, R. A. Using Reduced Catalysts for Oxidation Reactions: Mechanistic Studies of the ″Periana-Catalytica″ System for CH4 Oxidation. J. Am. Chem. Soc. 2013, 135, 14644−14658.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02988. Experimental details and additional characterizations (PDF)

■

REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (L.-B.S.). E

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (11) Jiang, C.; Hara, K.; Fukuoka, A. Low-Temperature Oxidation of Ethylene over Platinum Nanoparticles Supported on Mesoporous Silica. Angew. Chem., Int. Ed. 2013, 52, 6265−6268. (12) Anpo, M.; Takeuchi, M. The Design and Development of Highly Reactive Titanium Oxide Photocatalysts Operating under Visible Light Irradiation. J. Catal. 2003, 216, 505−516. (13) Liu, J.; Zou, S.; Li, S.; Liao, X.; Hong, Y.; Xiao, L.; Fan, J. A General Synthesis of Mesoporous Metal Oxides with Well-Dispersed Metal Nanoparticles Via a Versatile Sol-Gel Process. J. Mater. Chem. A 2013, 1, 4038−4047. (14) Dhar, S.; Daniel, W. L.; Giljohann, D. A.; Mirkin, C. A.; Lippard, S. J. Polyvalent Oligonucleotide Gold Nanoparticle Conjugates as Delivery Vehicles for Platinum(Iv) Warheads. J. Am. Chem. Soc. 2009, 131, 14652−14653. (15) Mayeda, M. K.; Kuan, W. F.; Young, W. S.; Lauterbach, J. A.; Epps, T. H., III Controlling Particle Location with Mixed Surface Functionalities in Block Copolymer Thin Films. Chem. Mater. 2012, 24, 2627−2634. (16) Tschulik, K.; Ngamchuea, K.; Ziegler, C.; Beier, M. G.; Damm, C.; Eychmueller, A.; Compton, R. G. Core-Shell Nanoparticles: Characterizing Multifunctional Materials Beyond Imaging-Distinguishing and Quantifying Perfect and Broken Shells. Adv. Funct. Mater. 2015, 25, 5149−5158. (17) Zhu, J. J.; Wang, T.; Xu, X. L.; Xiao, P.; Li, J. L. Pt Nanoparticles Supported on SBA-15: Synthesis, Characterization and Applications in Heterogeneous Catalysis. Appl. Catal., B 2013, 130-131, 197−217. (18) Rioux, R. M.; Song, H.; Hoefelmeyer, J. D.; Yang, P.; Somorjai, G. A. High-Surface-Area Catalyst Design: Synthesis, Characterization, and Reaction Studies of Platinum Nanoparticles in Mesoporous SBA15 Silica. J. Phys. Chem. B 2005, 109, 2192−2202. (19) Wang, Y.; Ren, J. W.; Deng, K.; Gui, L. L.; Tang, Y. Q. Preparation of Tractable Platinum, Rhodium, and Ruthenium Nanoclusters with Small Particle Size in Organic Media. Chem. Mater. 2000, 12, 1622−1627. (20) Song, H.; Rioux, R. M.; Hoefelmeyer, J. D.; Komor, R.; Niesz, K.; Grass, M.; Yang, P. D.; Somorjai, G. A. Hydrothermal Growth of Mesoporous SBA-15 Silica in the Presence of PVP-Stabilized Pt Nanoparticles: Synthesis, Characterization, and Catalytic Properties. J. Am. Chem. Soc. 2006, 128, 3027−3037. (21) Liu, X. Y.; Sun, L. B.; Lu, F.; Liu, X. D.; Liu, X. Q. LowTemperature Generation of Strong Basicity Via an Unprecedented Guest-Host Redox Interaction. Chem. Commun. 2013, 49, 8087−8089. (22) Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom Pores. Science 1998, 279, 548−552. (23) Kang, Y. H.; Liu, X. D.; Yan, N.; Jiang, Y.; Liu, X. Q.; Sun, L. B.; Li, J. R. Fabrication of Isolated Metal-Organic Polyhedra in Confined Cavities: Adsorbents/Catalysts with Unusual Dispersity and Activity. J. Am. Chem. Soc. 2016, 138, 6099−6102. (24) Estudillo-Wong, L. A.; Luo, Y.; Diaz-Real, J. A.; Alonso Vante, N. Enhanced Oxygen Reduction Reaction Stability on Platinum Nanoparticles Photo-Deposited onto Oxide-Carbon Composites. Appl. Catal., B 2016, 187, 291−300. (25) Yin, Y.; Yang, Z.-F.; Wen, Z.-H.; Yuan, A.-H.; Liu, X.-Q.; Zhang, Z.-Z.; Zhou, H. Modification of as Synthesized Sba-15 with Pt Nanoparticles: Nanoconfinement Effects Give a Boost for Hydrogen Storage at Room Temperature. Sci. Rep. 2017, 7, 4509. (26) Zhong, Z.; Lin, J.; Teh, S. P.; Teo, J.; Dautzenberg, F. M. A Rapid and Efficient Method to Deposit Gold Particles onto Catalyst Supports and Its Application for CO Oxidation at Low Temperatures. Adv. Funct. Mater. 2007, 17, 1402−1408. (27) Sun, L. B.; Li, J. R.; Lu, W.; Gu, Z. Y.; Luo, Z.; Zhou, H. C. Confinement of Metal-Organic Polyhedra in Silica Nanopores. J. Am. Chem. Soc. 2012, 134, 15923−15928. (28) Yin, Y.; Jiang, W. J.; Liu, X. Q.; Li, Y. H.; Sun, L. B. Dispersion of Copper Species in a Confined Space and Their Application in Thiophene Capture. J. Mater. Chem. 2012, 22, 18514−18521.

(29) Ewing, C. S.; Hartmann, M. J.; Martin, K. R.; Musto, A. M.; Padinjarekutt, S. J.; Weiss, E. M.; Veser, G.; McCarthy, J. J.; Johnson, J. K.; Lambrecht, D. S. Structural and Electronic Properties of Pt-13 Nanoclusters on Amorphous Silica Supports. J. Phys. Chem. C 2015, 119, 2503−2512.

F

DOI: 10.1021/acs.inorgchem.7b02988 Inorg. Chem. XXXX, XXX, XXX−XXX