CeO2 Catalysts for

2 days ago - Nanostructured PdO/CeO2 supported on mesoporous SBA-15 silica was synthesized using a combination of incipient wetness impregnation and s...
1 downloads 11 Views 2MB Size
Download PDF
Research Article www.acsami.org

Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Mesoporous Silica-Supported Nanostructured PdO/CeO2 Catalysts for Low-Temperature Methane Oxidation Yiling Dai,† Vanama Pavan Kumar,† Chujie Zhu,‡ Mark J. MacLachlan,*,† Kevin J. Smith,*,‡ and Michael O. Wolf*,† †

Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, British Columbia V6T 1Z3, Canada

‡

S Supporting Information *

ABSTRACT: Nanostructured PdO/CeO2 supported on mesoporous SBA-15 silica was synthesized using a combination of incipient wetness impregnation and surface-assisted reduction. After calcination, the materials showed good activity as catalysts for the low-temperature oxidation of methane, with a sample having 5 wt % Pd loading showing 50% conversion to CO2 at ∼290 °C and complete conversion below 360 °C. The stability of catalysts in the presence of water was studied. The formation of Pd(0) during the methane oxidation reaction increases the oxygen vacancies on the surface of catalysts, improving the catalytic activity. KEYWORDS: methane oxidation, double deposition approach, mesoporous silica, ceria, palladium oxide °C.10 Our group reported the preparation of nanostructured PdO/CeO2 by a new “surface-assisted reduction” (SAR) method.32 In this approach, reactive formate groups on the surface of nanostructured cerium formate (CF) act to reduce Pd2+ onto the surface, yielding nanostructured CeO2 substrates coated with highly dispersed PdO after calcination. These catalysts show 50% conversion for the oxidation of methane below 300 °C. The activity of heterogeneous catalysts is influenced by many factors, including particle size,33 and in many cases, nanoparticles give rise to the best catalytic performance;34 sintering, however, can reduce performance over time. Confining nanoparticle catalysts in mesoporous silica such as SBA-15 is an approach to overcome the sintering problem.35 In fact, SBA15 has been used to construct nanoparticles of various materials,36 some of which have been explored for catalysis.37 Here, we report the preparation of new nanostructured catalysts based on PdO/CeO2/PdO materials supported on SBA-15. These materials have been constructed using a novel double deposition approach, where SAR of Pd is carried out inside the channels of a mesoporous host for the first time. Importantly, the SBA-15 host constrains the size of the resulting Pd and CeO2 particles, whereas the SAR ensures excellent distribution of Pd on the nanostructured CeO2. The materials are evaluated for LTMOX catalysis.

1. INTRODUCTION Natural gas, composed primarily of methane, is a plentiful, cleaner alternative to gasoline and diesel as it results in the emission of less CO2 per unit energy produced.1−4 However, methane is a potent greenhouse gas, with a global warming potential more than 20 times greater than that of carbon dioxide.5 Consequently, managing the unburned methane expelled in the exhaust of natural gas engines is an important consideration for further expansion in the use of natural gas vehicles.6 Owing to the lack of a dipole moment and strong C−H bond strength (440 kJ mol−1),7 methane is the least reactive hydrocarbon and is not readily oxidized by conventional catalytic convertors.8 Efficient catalytic materials for lowtemperature methane oxidation (LTMOX) require low lightoff temperatures (99% conversion at 400 °C, with a 5% decrease in conversion after reaction for 50 h (gas hourly space velocity (GHSV) = 30 000 mL h−1 g−1). For the catalysts reported here with 1% Pd loading, 90% conversion is obtained at 370 °C but this recovers to 100% conversion after

oxidation, showing both Pd and PdO peaks. In contrast, only PdO was observed by XPS of the fresh catalysts. This indicates that the reaction gas reduced the PdO to Pd.44 Although Pd(0) was observed by XPS, crystalline Pd was not observed in the PXRD of the used catalyst. The Pd may be present in nanoparticles that are too small to show diffraction. Moreover, the Ce 3d peaks for the fresh sample show a pure CeO2 pattern with about 6% Ce3+.45 For the used catalyst, the percentage of Ce3+ increased to about 10%, resulting in weakening of the Ce−O bond and increased oxygen mobility.45 The formation of Pd during the reaction increases the number of oxygen vacancies on the surface. Both the PdO and H

DOI: 10.1021/acsami.7b13408 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 11. XPS spectra for PdCFPdSBA-15(M) 5% Pd before and after the thermal stability test. (a) Pd 3d peaks, (b) Ce 3d peaks (red solid circles represent Ce 3d3/2, and blue solid circles represent Ce 3d5/2) for fresh catalysts. (c) Pd 3d peaks, (d) Ce 3d peaks for used catalysts.

attributed to the small size and good distribution of Pd on CeO2 and also PdO/CeO2/PdO on SBA-15. In addition, the water stability of the catalysts was studied. After the injection of water, the activity clearly decreased. However, the activity increased gradually afterward and was even better than that for fresh catalysts after water was removed. The improved catalytic activity during the reaction is attributed to the formation of Pd(0), which increased oxygen vacancies. These results demonstrate a new way to make stable methane oxidation catalysts that may be useful for catalytic converters in natural gas engines.

Table 4. XPS Data for Catalysts of PdCFPdSBA-15(M) 5% Pd before and after the Thermal Stability Test element

catalysts

Ce

fresh used

Pd

fresh used

binding energy (eV) 883.7, 886.6, 883.3, 886.0, 337.4, 337.3, 336.2,

889.5, 899.3, 902.1, 908.3, 917.8 905.6 889.1, 899.0, 901.7, 908.0, 917.5 904.5 342.6 342.6 340.7

oxidation state +4 +3 +4 +3 +2 +2 0

■

20 h of exposure to water (GHSV = 180 000 mL h−1 g−1). Yang et al.48 reported the synthesis of Au@PdOx embedded in Co3O4 nanorods with 2.44 wt % Pd loading; this catalyst achieved 90% conversion at 344 °C (GHSV = 60 000 mL h−1 g−1). The catalysts reported here with 1% Pd loading achieved 100% conversion at 355 °C after water stability tests under much higher GHSV.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b13408. Silica loading calculations, IR spectra, and PXRD patterns for the catalysts (PDF)

■

4. CONCLUSIONS In summary, nanoparticles of PdO/CeO2/PdO supported on SBA-15 were prepared by impregnation and surface-assisted reduction. Using the SAR method within the pores of a mesoporous host (SBA-15) allowed us to constrain the size of the catalytic nanoparticles and to obtain an even distribution of the catalyst inside the channels of silica. The catalyst system PdO/CeO2/PdO on SBA-15 shows high activity for lowtemperature methane oxidation, and the high activity is

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (M.J.M.). *E-mail: [email protected] (K.J.S.). *E-mail: [email protected] (M.O.W.). ORCID

Mark J. MacLachlan: 0000-0002-3546-7132 Kevin J. Smith: 0000-0001-6008-0223 Michael O. Wolf: 0000-0003-3076-790X I

DOI: 10.1021/acsami.7b13408 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces Notes

(17) Chin, Y.-H.; Buda, C.; Neurock, M.; Iglesia, E. Selectivity of Chemisorbed Oxygen in C-H Bond Activation and CO Oxidation and Kinetic Consequences for CH4-O2 Catalysis on Pt and Rh Clusters. J. Catal. 2011, 283, 10−24. (18) Chin, Y.-H.; Buda, C.; Neurock, M.; Iglesia, E. Reactivity of Chemisorbed Oxygen Atoms and their Catalytic Consequences during CH4-O2 Catalysis on Supported Pt Clusters. J. Am. Chem. Soc. 2011, 133, 15958−15978. (19) Arroyo-Ramírez, L.; Chen, C.; Cargnello, M.; Murray, C. B.; Gorte, R. J. A Comparison of Hierarchical Pt@ CeO2/Si-Al2O3 and Pd@ CeO2/Si-Al2O3. Catal. Today 2015, 253, 137−141. (20) Arandiyan, H.; Dai, H.; Ji, K.; Sun, H.; Li, J. Pt Nanoparticles Embedded in Colloidal Crystal Template Derived 3D Ordered Macroporous Ce0.6Zr0.3Y0.1O2: Highly Efficient Catalysts for Methane Combustion. ACS Catal. 2015, 5, 1781−1793. (21) Setiawan, A.; Kennedy, E. M.; Dlugogorski, B. Z.; Adesina, A. A.; Stockenhuber, M. The stability of Co3O4, Fe2O3, Au/Co3O4 and Au/ Fe2O3 Catalysts in the Catalytic Combustion of Lean Methane Mixtures in the Presence of Water. Catal. Today 2015, 258, 276−283. (22) Bera, P.; Hegde, M. S. Characterization and Catalytic Properties of Combustion Synthesized Au/CeO2 Catalyst. Catal. Lett. 2002, 79, 75−81. (23) Feng, Y. Z.; Rao, P. M.; Kim, D. R.; Zheng, X. L. Methane Oxidation over Catalytic Copper Oxides Nanowires. Proc. Combust. Inst. 2011, 33, 3169−3175. (24) Hu, W.; Lan, J.; Guo, Y.; Cao, X.-M.; Hu, P. Origin of Efficient Catalytic Combustion of Methane over Co3O4 (110): Active Lowcoordination Lattice Oxygen and Cooperation of Multiple Active Sites. ACS Catal. 2016, 6, 5508−5519. (25) Pontelli, G. C.; Reolon, R. P.; Alves, A. K.; Berutti, F. A.; Bergmann, C. P. Application of Cerium Oxide Electrospun Fibers in the Catalytic Combustion of Methane. Appl. Catal., A 2011, 405, 79− 83. (26) Wang, X.; Xie, Y. C. Total Oxidation of Methane Over La, Ce and Y Modified Manganese Oxide Catalysts. React. Kinet. Catal. Lett. 2000, 71, 3−11. (27) Barbato, P. S.; Benedetto, A. D.; Sarli, V. D.; Landi, G.; Pirone, R. High-pressure Methane Combustion over a Perovskite Catalyst. Ind. Eng. Chem. Res. 2012, 51, 7547−7558. (28) Popescu, I.; Boudjemaa, A.; Helaili, N.; Bessekhouad, Y.; Tudorache, M.; Bachari, K.; Marcu, I. C. Study of the Electrical and Catalytic Properties of Spinels with CuFe2−xMnxO4 Composition (x = 0, 0.4, 0.8, 1.6, and 2). Appl. Catal., A 2015, 504, 29−36. (29) Zheng, J. D.; Ren, X. G.; Song, Y. J.; Ge, X. T. Catalytic Combustion of Methane over Iron- and Manganese-substituted Lanthanum Hexaaluminates. React. Kinet. Catal. Lett. 2009, 97, 109− 114. (30) Monai, M.; Montini, T.; Chen, C.; Fonda, E.; Gorte, R. J.; et al. Methane Catalytic Combustion over Hierarchical Pd@CeO2/SiAl2O3: Effect of the Presence of Water. ChemCatChem 2015, 7, 2038−2046. (31) Adijanto, L.; Bennett, D. A.; Chen, C.; Yu, A. S.; Cargnello, M.; Fornasiero, P.; Gorte, R. J.; Vohs, J. M. Exceptional Thermal Stability of Pd@ CeO2 Core-shell Catalyst Nanostructures Grafted onto an Oxide Surface. Nano Lett. 2013, 13, 2252−2257. (32) Gomathi, A.; Vickers, S. M.; Gholami, R.; Alyani, M.; Man, R. W. Y.; MacLachlan, M. J.; Smith, K. J.; Wolf, M. O. Nanostructured Materials Prepared by Surface-Assisted Reduction: New Catalysts for Methane Oxidation. ACS Appl. Mater. Interfaces 2015, 7, 19268− 19273. (33) Qian, X.; Kuwahara, Y.; Mori, K.; Yamashita, H. Silver Nanoparticles Supported on CeO2-SBA-15 by Microwave Irradiation Possess Metal-Support Interactions and Enhanced Catalytic Activity. Chem. - Eur. J. 2014, 20, 15746−15752. (34) Chiang, C.-W.; Wang, A.-Q.; Mou, C.-Y. CO Oxidation Catalyzed by Gold Nanoparticles Confined in Mesoporous Aluminosilicate Al-SBA-15: Pretreatment Methods. Catal. Today 2006, 117, 220−227.

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful to the Natural Sciences and Engineering Research Council (NSERC) of Canada and Westport Fuel Systems Inc. for funding this research. We are especially thankful to Dr. Sandeep Munshi for helpful comments and support. Y.D. is grateful to UBC for a four year fellowship.

■

REFERENCES

(1) Choudhary, T. V.; Banerjee, S.; Choudhary, V. R. Catalysts for Combustion of Methane and Lower Alkanes. Appl. Catal., A. 2002, 234, 1−23. (2) Chen, J. H.; Arandiyan, H.; Gao, X.; Li, J. H. Recent Advances in Catalysts for Methane Combustion. Catal. Surv. Asia 2015, 19, 140− 171. (3) Xu, J.; Ouyang, L.; Mao, W.; Yang, X.-J.; Xu, X.-C.; Su, J.-J.; Zhuang, T.-Z.; Li, H.; Han, Y.-F. Operando and Kinetic Study of LowTemperature, Lean-Burn Methane Combustion over a Pd/γ-Al2O3 Catalyst. ACS Catal. 2012, 2, 261−269. (4) Wang, W.; Yuan, F.; Niu, X.; Zhu, Y. Preparation of Pd Supported on La (Sr)-Mn-O Perovskite by Microwave Irradiation Method and its Catalytic Performances for the Methane Combustion. Sci. Rep. 2016, 6, No. 19511. (5) Shen, J.; Hayes, R. E.; Wu, X.; Semagina, N. 100° Temperature Reduction of Wet Methane Combustion: Highly Active Pd-Ni/Al2O3 Catalyst versus Pd/NiAl2O4. ACS Catal. 2015, 5, 2916−2920. (6) Choudhary, V. R.; Deshmukh, G. M.; Pataskar, S. G. LowTemperature Complete Combustion of a Dilute Mixture of Methane and Propane over Transition-Metal-Doped ZrO2 Catalysts: Effect of the Presence of Propane on Methane Combustion. Environ. Sci. Technol. 2005, 39, 2364−2368. (7) Horn, R.; Schlogl, R. Methane Activation by Heterogeneous Catalysis. Catal. Lett. 2015, 145, 23−39. (8) Choudhary, V. R.; Uphade, B. S.; Pataskar, S. G.; Keshavaraja, A. Low-Temperature Complete Combustion of Methane over Mn-, Co-, and Fe-Stabilized ZrO2. Angew. Chem., Int. Ed. 1996, 35, 2393−2395. (9) Gélin, P.; Primet, M. Complete Oxidation of Methane at Low Temperature over Noble Metal based Catalysts: a Review. Appl. Catal., B 2002, 39, 1−37. (10) Cargnello, M.; Jaén, J. J. D.; Garrido, J. C. H.; Bakhmutsky, K.; Montini, T.; Gámez, J. J. C.; Gorte, R. J.; Fornasiero, P. Exceptional Activity for Methane Combustion over Modular Pd@ CeO2 Subunits on Functionalized Al2O3. Science 2012, 337, 713−717. (11) Jin, J.; Li, C.; Tsang, C.-W.; Xu, B.; Liang, C. Catalytic Combustion of Methane over Pt-Ce Oxides under Scarce Oxygen Condition. Ind. Eng. Chem. Res. 2016, 55, 2293−2301. (12) Willis, J. J.; Goodman, E. D.; Wu, L.; Riscoe, A. R.; Martins, P.; Tassone, C. J.; Cargnello, M. Systematic Identification of Promoters for Methane Oxidation Catalysts Using Size-and CompositionControlled Pd-Based Bimetallic Nanocrystals. J. Am. Chem. Soc. 2017, 139, 11989−11997. (13) Onn, T. M.; Zhang, S.; Arroyo-Ramirez, L.; Chung, Y.-C.; Graham, G. W.; Pan, X.; Gorte, R. J. Improved Thermal Stability and Methane-Oxidation Activity of Pd/Al2O3 Catalysts by Atomic Layer Deposition of ZrO2. ACS Catal. 2015, 5, 5696−5701. (14) Gholami, R.; Alyani, M.; Smith, K. J. Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters. Catalysts 2015, 5, 561− 594. (15) Chin, Y.-H; Buda, C.; Neurock, M.; Iglesia, E. Consequences of Metal-oxide Interconversion for C-H bond Activation during CH4 Reactions on Pd Catalysts. J. Am. Chem. Soc. 2013, 135, 15425−15442. (16) Chin, Y.-H; Iglesia, E. Elementary Steps, the Role of Chemisorbed Oxygen, and the Effects of Cluster Size in Catalytic CH4-O2 Reactions on Palladium. J. Phys. Chem. C 2011, 115, 17845− 17855. J

DOI: 10.1021/acsami.7b13408 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces (35) Yeh, Y.-Q.; Lin, H.-P.; Tang, C.-Y.; Mou, C.-Y. Mesoporous Silica SBA-15 Sheet with Perpendicular Nanochannels. J. Colloid Interface Sci. 2011, 362, 354−366. (36) Fan, J.-W.; Jiang, X.; Min, H.-Y.; Li, D.-D.; Ran, X.-Q.; Zou, L.Y.; Sun, Y.; Li, W.; Yang, J.-P.; Teng, W.; et al. Facile Preparation of Cu-Mn/CeO2/SBA-15 Catalysts using Ceria as an Auxiliary for Advanced Oxidation Processes. J. Mater. Chem. A 2014, 2, 10654− 10661. (37) Chiang, C.-W.; Wang, A.-Q.; Wan, B.-Z.; Mou, C.-Y. High Catalytic Activity for CO Oxidation of Gold Nanoparticles Confined in Acidic Support Al-SBA-15 at Low Temperatures. J. Phys. Chem. B 2005, 109, 18042−18047. (38) Tao, Q.; Xu, Z.-Y.; Wang, J.-H.; Liu, F.-L; Wan, H.-Q.; Zheng, S.-R. Adsorption of Humic Acid to Aminopropyl Functionalized SBA15. Microporous Mesoporous Mater. 2010, 131, 177−185. (39) Frost, R. L.; Yang, J.; Ding, Z. Raman and FTIR Spectroscopy of Natural Oxalates: Implications for the Evidence of Life on Mars. Chin. Sci. Bull. 2003, 48, 1844−1852. (40) MacLachlan, M. J.; Aroca, P.; Coombs, N.; Manners, I.; Ozin, G. A. Ring-Opening Polymerization of a [1]Silaferrocenophane Within the Channels of Mesoporous Silica: Poly(ferrocenylsilane)-MCM-41 Precursors to Magnetic Iron Nanostructures. Adv. Mater. 1998, 10, 144−149. (41) Larcher, D.; Gérand, B.; Tarascon, J.-M. Synthesis and Electrochemical Performances of Li1+yMn2−yO4 Powders of Welldefined Morphology. J. Solid State Electrochem. 1998, 2, 137−145. (42) Zhai, Y.; Zhang, S.; Pang, H. Preparation, Characterization and Photocatalytic Activity of CeO2 Nanocrystalline using Ammonium Bicarbonate as Precipitant. Mater. Lett. 2007, 61, 1863−1866. (43) Ciuparu, D.; Perkins, E.; Pfefferle, L. In Situ DR-FTIR Investigation of Surface Hydroxyls on γ-Al2O3 Supported PdO Catalysts during Methane Combustion. Appl. Catal., A 2004, 263, 145−153. (44) Ciuparu, D.; Lyubovsky, M. R.; Altman, E.; Pfefferle, L. D.; Datye, A. Catalytic Combustion of Methane Over Palladium-Based Catalysts. Catal. Rev. 2002, 44, 593−649. (45) Venezia, A. M.; Pantaleo, G.; Longo, A.; Di Carlo, G.; Casaletto, M. P.; Liotta, F. L.; Deganello, G. Relationship between Structure and CO Oxidation Activity of Ceria-supported Gold Catalysts. J. Phys. Chem. B 2005, 109, 2821−2827. (46) Zou, X.; Rui, Z.; Ji, H. Core-Shell NiO@PdO Nanoparticles Supported on Alumina as an Advanced Catalyst for Methane Oxidation. ACS Catal. 2017, 7, 1615−1625. (47) Zou, X.; Rui, Z.; Song, S.; Ji, H. Enhanced Methane Combustion Performance over NiAl2O4-interface-Promoted Pd/γ-Al2O3. J. Catal. 2016, 338, 192−201. (48) Yang, N.; Liu, J.; Sun, Y.; Zhu, Y. Au@PdOx with a PdOx-rich Shell and Au-rich Core Embedded in Co3O4 Nanorods for Catalytic Combustion of Methane. Nanoscale 2017, 9, 2123−2128.

K

DOI: 10.1021/acsami.7b13408 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX