Carbon Coating for Improved Hydrothermal Stability of Silica Supp

University of New Mexico UNM Digital Repository Nanoscience and Microsystems ETDs Engineering ETDs 2-8-2011 Carbon Coating for Improved Hydrothermal Stability of Silica Supports Amanda Lynn Staker Follow this and additional works at: https://digitalrepository.unm.edu/nsms_etds Recommended Citation Staker, Amanda Lynn "Carbon Coating for Improved Hydrothermal Stability of Silica Supports." (2011) https://digitalrepository.unm.edu/nsms_etds/28 This Thesis is brought to you for free and open access by the Engineering ETDs at UNM Digital Repository It has been accepted for inclusion in Nanoscience and Microsystems ETDs by an authorized administrator of UNM Digital Repository For more information, please contact disc@unm.edu Carbon Coating for Improved Hydrothermal Stability of Silica Supports by Amanda Lynn Staker B.A., ACS Chemistry, Gustavus Adolphus College, 2009 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Nanoscience and Microsystems The University of New Mexico Albuquerque, New Mexico December, 2010 c 2010, Amanda Lynn Staker iii Dedication To my mom, without her continued encouragement and support, I would not be where I am today I’m forever grateful for everything she has done for me and for what she continues to for me iv Acknowledgments I would to acknowledge my advisor, Dr Abhaya Datye, for everything he has done for me over the past year as his student and for his continued guidance and support I would also like to thank him for accepting me as an undergraduate researcher for the summer of 2008 as an REU student, which ultimately led me to the University of New Mexico for graduate school I would also like to thank Hien Pham, who has helped me with the microscopy and the synthesis for this project over the past year Thanks also to my REU student, Andrew Dick from the University of Kansas, for all the work he has done in the laboratory over his short stay in New Mexico and for helping troubleshoot problems throughout the synthesis and characterization process I would also like to thank the members of the Datye research group; Patrick Burton, Eric Peterson, Angelica Sanchez, Jonathan Paiz, Ulises Martinez, Daniel Konopka, Tyne Johns, Elena Berliba-Vera, Adam Tsosie, Barr Halevi, Hien Pham, Sivakumar Challa and former members for their advice and guidance during my time as a graduate student as well as a REU student; Levi Houk, Andrew DeLaRiva, and Ron Goeke I would like to acknowledge the financial support of this work from the U.S National Science Foundation Engineering Research Center for Biorenewable Chemicals under Grant Number EEC-0813570 and from the U.S National Science Foundation Partnerships for International Research and Education under Grant Number OISE-0730277 The work also made use of the electron microscopy facilities at the University of New Mexico which are supported by the NSF EPSCOR and NSF NNIN grants Also my committee, Dr Abhaya Datye (chair), Dr Deborah Evans, and Dr Hua Guo v Carbon Coating for Improved Hydrothermal Stability of Silica Supports by Amanda Lynn Staker ABSTRACT OF THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Nanoscience and Microsystems The University of New Mexico Albuquerque, New Mexico December, 2010 Carbon Coating for Improved Hydrothermal Stability of Silica Supports by Amanda Lynn Staker B.A., ACS Chemistry, Gustavus Adolphus College, 2009 M.S., Nanoscience and Microsystems, University of New Mexico, 2010 Abstract A large number of industrial chemicals produced today come from petroleum-based feedstocks With these feedstocks dwindling, it is necessary to develop alternative ways to produce these chemicals from biorenewable feedstocks The move from the current petroleum-based chemical industry to a biorenewable chemical industry will build on a current platform chemical approach, where a small number of key chemical intermediates produced from biorenewable sources will serve as the platform to produce a broad range of chemical products Since carbon is necessary to produce these chemicals, biomass, with its short formation time, must become the feedstock for the chemical industry Since the new feedstock is in aqueous phase the catalyst supports used currently in the petroleumbased chemical industry, such as silica and alumina, will not work because they are not hydrothermally stable Silica and alumina are used as catalyst supports because they are mechanically stable, have large surface areas, and synthesis methods are well established but they tend to react with water and lose their integrity during aqueous phase reactions at elevated temperatures Mesoporous carbons are an attractive alternative to mesoporous vii oxides because they are thermally and chemically stable except in the presence of oxygen The problem with these mesoporous carbons is they lack mechanical strength and their pore structure cannot be as easily tailored as that of the oxide supports The central objective of this work was to integrate the benefits of both the mesoporous oxides (mechanical stability) and the mesoporous carbons (thermal and chemical stability) to produce hydrothermally stable catalyst supports The approach used to combine the benefits of these supports was to deposit a thin layer of carbon within the pores of a mesoporous silica By doing this, the mechanical stability of the mesoporous silica was retained and the support became thermally and chemically stable due to the thin layer of carbon on the silica support The characterization techniques used to analyze the carbon-coated silica supports were FTIR, DRIFT, TGA, TEM, STEM, EFTEM, HRTEM, nitrogen adsorption surface area analysis, and hydrothermal treatments This study successfully showed carbon from different precursors could be bound to the surface of Stăober spheres, a model silica support, and to the surface and within the pores of SBA-15, a mesoporous silica viii Contents List of Figures xii List of Tables xix Glossary xx Introduction 1.1 Introduction to the Chemical Industry 1.1.1 Petroleum-Based Chemical Industry 1.1.2 Biorenewable Chemical Industry Motivation 1.2.1 Hydrothermally Stable Catalyst Supports 1.3 Problem Statement 1.4 Hypothesis 1.2 Literature and Background ix Contents 2.1 Mesoporous Silica Materials 2.2 Mesoporous Carbon Materials 2.2.1 Hard Template Method 10 2.2.2 Soft Template Method 12 2.3 Model Silica Spherical Materials 15 2.4 Macroporous Carbon Materials 15 2.5 Mesoporous Silica/Carbon Composites 16 Materials and Methods 19 3.1 Experimental 19 3.1.1 Synthesis of Silica Supports 19 3.1.2 Synthesis of Carbon-Coated Silica Supports 20 Characterization 25 3.2 Carbon Coated Model Silica Supports 27 4.1 Stăober Spheres 27 4.2 Stăober Spheres/Carbon Coatings 31 4.2.1 Stăober Spheres Coated with 2,3-dihydroxynaphthalene (DN) 31 4.2.2 Stăober Spheres Coated with Sucrose 35 Carbon Coated Mesoporous Silica Supports 41 5.1 41 SBA-15 x Chapter Carbon Coated Mesoporous Silica Supports surface of the SBA-15 when heated to elevated temperatures It was also shown that the SBA-15 coated with DN was hydrothermally stable because the surface area of the support was retained 5.2.2 SBA-15 Coated with Sucrose Thermogravimetric Analysis (TGA) was performed on sucrose to measure the weight loss of the support over time and temperature in the previous section Then TGA was performed on the SBA-15 coated with sucrose by the evaporation of the solvent exposed to air method to measure the weight loss of the support over time and temperature Figure 5.9 shows the weight percent loss and the heat flow in the instrument during the experiment The TGA spectrum of the SBA-15 coated with sucrose shows the melting point of sucrose is at 190◦ C where there is a peak in the heat flow, at 250◦ C is where sucrose decomposes and there is also a peak in the heat flow at that point, and after heating to 1000◦ C a small amount of carbon was still present Fourier Transform Infrared (FTIR) Spectroscopy was performed on the SBA-15 coated with sucrose to measure the vibrations of the functional groups on the surface of the silica Figure 5.9 is a spectrum of the SBA-15 coated with sucrose that was collected with an attenuated total reflectance (ATR) attachment The silica stretching and bending modes are in Table 5.1 The carbon stretching and bending modes are: the O-H stretch are isolated peaks at 3600-3650 cm−1 and broad O-H stretch at 3200-3500 cm−1 , the C-H arene stretch is at 3030 cm−1 , the C-H -CH2 - bending is at 1450-1475 cm−1 , the C-O ether stretch is at 1200-1250 cm−1 , the C-O alcohol stretch is at 1000-1100 cm−1 , and the C-H arene bends are isolated peaks at 750 and 900 cm−1 (Table 4.3) For the sample heated to 300◦ C it shows there is carbon still present on the surface of the SBA-15 (Figure 5.9) Nitrogen adsorption was performed on the SBA-15 coated with sucrose to measure the surface area (Table 5.2.2) From the data it shows that when SBA-15 is heated to a high 50 Chapter Carbon Coated Mesoporous Silica Supports Figure 5.9: SBA-15 coated with sucrose: left) TGA, at 100◦ C the adsorbed water on the surface desorbs, the melting point of sucrose is at 190◦ C where there is a peak in the heat flow, at 250◦ C is where sucrose decomposes and there is also a peak in the heat flow at that point, and after heating to 1000◦ C a small amount of carbon was still present, and right) FTIR spectrum: blue) SBA-15, violet) as prepared SBA-15 coated with sucrose, and red) SBA-15 coated with sucrose heated to 300◦ C in N2 temperature the surface area decreases by a little more than half When the samples were coated with sucrose the surface area decreases from the original SBA-15 sample, which is expected because the surface is getting covered with carbon When the SBA-15 was coated with sucrose and heated to 400◦ C the surface area was close to the purely heated SBA-15 but still higher because the carbon is coating the SBA-15 and the SBA-15 structure is more stable at 400◦ C than at 900◦ C Surface Area of SBA-15 Sample SBA-15 SBA-15 and Sucrose As-Prepared SBA-15 and Sucrose Heated to 200◦ C SBA-15 and Sucrose Heated to 300◦ C SBA-15 and Sucrose Heated to 400◦ C SBA-15 Heated to 900◦ C Surface Area 590 m2 g−1 118 m2 g−1 121 m2 g−1 166 m2 g−1 346 m2 g−1 278 m2 g−1 Table 5.3: The surface area of SBA-15 coated with sucrose 51 Chapter Carbon Coated Mesoporous Silica Supports From the FTIR DRIFT cell data it showed that after heating the SBA-15 to 600◦ C there were no hydroxyl groups present on the surface for the carbon to bind with, but it was likely that hydroxyl groups were still present within the pores of the SBA-15 for the carbon to bind with From the other data above it has been shown that carbon in the form of DN and sucrose can be bound to the surface and within the pores of SBA-15 The TGA data showed that SBA-15 coated with DN and sucrose had a small amount of carbon still present after heating to 1000◦ C The FTIR spectra showed carbon was still present on the surface of the SBA-15 when heated to elevated temperatures It has also been shown that SBA-15 coated with DN has been stabilized for hydrothermal treatments This study has successfully shown that carbon from different precursors can be bound to the surface and within the pores of SBA-15 52 Chapter Summary and Conclusions Two types of silica supports were studied, a model silica support (Stăober spheres) that consists of spherical particles of silica which make it easy to see the carbon coating and a high surface area mesoporous silica (SBA-15) These silica supports were coated with two different carbon precursors (2,3-dihydroxynaphthalene (DN) and sucrose) The FTIR spectra of the pure Stăober spheres showed that after heating the spheres to 600◦ C there were no hydroxyl groups present on the surface for the carbon to bind with, which explains why after heating to temperatures higher than 600◦ there was no carbon bound to the surface of the Stăober spheres Heating the carbon precursors in an pure nitrogen atmosphere in a thermogravimetric analyzer (TGA) showed complete loss of DN after heating to 500◦ C while the pure sucrose showed some of the carbon survived up to 1000◦ C, which means sucrose is more thermally stable than DN The TGA data of the Stăober spheres coated with DN showed carbon was not present on the surface of the Stăober spheres after heating to 1000 C The TGA data of the Stăober spheres coated with sucrose showed that most of the carbon was gone by 400◦ C but a a small amount of carbon was still present after heating to 1000◦ C The FTIR spectra of the Stăober spheres coated with DN showed that carbon was still 53 Chapter Summary and Conclusions present on the surface of the spheres when heated to lower temperatures but once it was heated to elevated temperatures all the carbon was removed from the surface The FTIR spectra of the Stăober spheres coated with sucrose showed that carbon was also still present on the surface of the spheres when heated to lower temperatures The STEM images of both the DN and sucrose coated Stăober spheres also showed there was carbon present on the surface of the Stăober spheres after heating lower temperatures The TEM/EFTEM composite images clearly shows there was a thin layer of carbon on the surface of the Stăober spheres after heating to lower temperatures for both the DN and sucrose coated Stăober spheres This study successfully showed carbon from different carbon precursors (DN and sucrose) were chemically bound to the surface of Stăober spheres at lower temperatures It was also shown that by depositing a thin layer of carbon on the surface of the Stăober spheres it became more hydrophobic in nature Mesoporous silica supports (SBA-15) were coated with the same carbon precursors as the Stăober spheres (DN and sucrose) The FTIR spectra of the pure SBA-15 showed that after heating the SBA-15 to 600◦ C there were no hydroxyl groups present on the surface for the carbon to bind with, but internal hydroxyls were still likely present within the pores of the SBA-15 The TGA data of the SBA-15 coated with DN showed that most of the carbon was gone by 300◦ C but a small amount remained even after heating to 1000◦ C The TGA data of the SBA-15 coated with sucrose showed that most of the carbon was gone by 400◦ C but a small amount remained even after heating to 1000◦ C The FTIR spectra of the SBA-15 coated with DN showed that carbon was still present on the surface of the SBA-15 after heating to lower temperatures, elevated temperatures, and after hydrothermal treatments The FTIR spectra of the SBA-15 coated with sucrose showed that carbon was still present on the surface of the SBA-15 after heating to lower temperatures The surface area of SBA-15 was determined by nitrogen adsorption and the surface of pure SBA-15 was determined to be 590 m2 g−1 The pure SBA-15 was heated to an elevated temperature to determine its thermal stability and the surface area was determined 54 Chapter Summary and Conclusions to be less than half the original surface area of SBA-15 The decrease in surface area was likely due to grain growth and sintering of the silica support and pure SBA-15 was shown to not be thermally stable When the SBA-15 was coated with DN or sucrose and heated to lower temperatures the surface area decreased from the original SBA-15 because the pores were getting filled with carbon As the SBA-15 coated with DN or sucrose was heated to higher temperatures the surface area started to increase due to the carbon precursor being decomposed The SBA-15 that was coated with DN and heated to elevated temperatures had a surface area close to the SBA-15 heated to an elevated temperature but the DN coated SBA-15 was still lower because the carbon was coating the SBA-15 The SBA15 coated with DN that was heated to an elevated temperature was also hydrothermally treated and the surface area was retained after the hydrothermal treatment This study has successfully shown that carbon from different carbon precursors (DN and sucrose) were chemically bound to the surface and within the pores of SBA-15 at elevated temperatures 55 Chapter Future Work The next step for this project would be to synthesize hydrothermally stable catalysts for a specific biorenewable acid catalyzed reaction, such as converting 1,2,6-hexanetriol (a biorenewable platform chemical) to 1,6-hexanediol (a biorenewable chemical product) in an aqueous environment at 200◦ C These hydrothermally stable catalysts will be synthesized by depositing nanosized metal on the supports The nanosized metal particles that could ultimately be used to produce the hydrothermally stable catalysts are Au, Pt-Re, Pt-Mo, for example The hydrothermally stable catalysts produced will then need be tested for catalytic activity, selectivity, conversion, and hydrothermal stability The catalytic activity of the catalyst will be measured by its turnover frequency (TOF), moles of 1,2,6-hexanetriol converted per mole of surface Au (for example) and per second The selectivity of the catalyst will be measured by the molar ratio of 1,6-hexanediol to 1,2,6hexanetriol converted The conversion of the reaction will be monitored with high performance liquid chromatography (HPLC) because HPLC will easily separate these chemicals in aqueous 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Nanoscience and Microsystems The University of New Mexico Albuquerque, New Mexico December, 2010 Carbon Coating for Improved Hydrothermal Stability of Silica Supports by Amanda Lynn Staker B.A., ACS