Progress 02/01/17 to 01/31/19
Outputs
Target Audience:
Nothing Reported
Changes/Problems:In the third and most ambious aim of this work ("Evaluate SAM-functionalized zeolite catalysts"), we were not success in functionalizing an acidic, zeolite catalyst. Every catalyst we attempted to functionalized with phophonic acid SAMs appeared to react with the phosphonic acid, breaking down. Thus, we were not able to functionalize any catalytic zeolite with a phosphonic acid self-assembled monolayer. This significantly hampered progress of this aim. By studying a variety of zeolites, we were able to find certain zeolites that were able to functionalized with phosphonic acid SAMs. One zeolite that we were able to routinely functionalize was Zeolite 5A. 5A is not used as a catalyst, but is used as a dessicant and in gas separations (selective adsorber). Thus, the direction of this project changed to focus on a non-catalytic zeolite, zeolite 5A. Though zeolite 5A is not used for reactions with alcohols, there are significant industrial interests in 5A due to its ability to separatesmall molecules like carbon dioxide and n-butane.The most obvious industrial usewould be to purify natural gas streams to remove water and carbon dioxide, thus increasing the heating value of the gas. Since zeolite 5A is not catalytic, we sought to understand how phosphonic acid SAMs would modify the rate of diffusion of gases into the zeolite. Understanding the diffusion properties of these highly porous materials is difficult and insights from these studies could be utilized in the future for research groups that are able to discover a means to reliably functionalized catalytic zeolites with SAMs. Reactions with catalytic zeolites are complex and require and understanding of molecules diffusing into the zeolite, reacting on a catalytic site, and diffusing out of the zeolite. Our work here helps provide an understanding of how SAMs can tune the diffusion properties of zeolties (but in a more simplified system, where no reaction is taking place). What opportunities for training and professional development has the project provided?The predoctoral fellowship programallowed me to grow as a scientist/engineer by attending professional conferences (North American Catalysis Society 2017 Meeting and 2017 Annual American Institute of Chemical Engineers meeting), foster collaborations inside and outside my home university, and mentor undergraduate and graduate students inresearch. Prior to receiving this fellowship, I was excited about the possibility of gaining experince in researching a certain class of metal oxide catalysts, called zeolites. Upon receiving the USDA-NIFA predoctoral fellowship, I fostered a collaboration with Dr. John Falconer of the Chemical and Biological Engineering Department at the University of Colorado, an expert in zeolitic materials. After much trial and error we developed a new zeolite materialwith the use of self-assembled monolayers. But, more importantly, the fellowship allowed me to collaborate with scientists and engineers of differing backgrounds and broadenmy scientific education. This project continued to foster other collaborations as well. For example, we sought to understand the location of self assembled monolayers on the zeolites, which led us to collaborating with experts at the Colorado School of Mines. Dr. Svitlana Pylypenko, of the Colorado School of Mines,is an expert in elemental maping using scanning tunneling microscopy and other tools. Additionally, we estabilished a collaboration with Georgia Institute of Technology with Dr. Carsten Sievers, where he was able to utilize a special type of nuclear magentic resonace to help describe the zeolite material structure. Overall, the predoctoral fellowship significantly improved my scientificbreadth and leadership skills. The collaboration with Dr. John Falconer also created two opportunites for me to mentor undergraduate researchers in a laboratory setting. This experience mentoring undergraduate researchers was educational and developed confidence in my research abilities and decision making skills. This experience mentoring undergraduate students led me to seek out more mentoring opportunites. I was given the opportunity to mentor a new graduate student, which ultimately resulted in higher productivity for both researchers and two publications. It was an immensley rewarding and fruitful experience. How have the results been disseminated to communities of interest?During the duration of the predoctoral fellowship the results of this research project were disseminated to the scientific community through two mechanisms: 1) presenting at conferences and 2) publications. The work developed during this fellowship was presented at the 2017 North American Catalysis Society meeting and 2017 American Institute of Chemical Engineers annual meeting. This work was also drafted into four manuscripts for publication (see publications) and a patent (see patents). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
1.Demonstrate the ability to form well-organized SAM layers on commercial metal oxide catalysts. We explored a variety of deposition methods for forming phosphonic acid and silane based self-assemblemed monlayers (SAMs) on many different metal oxides. We were able to form reliable SAMs of trimethylsilyl (a silane) on gamma-aluminum oxide (results described below of this material). Using phopshonic acids, we were able to functionalizea much wider variety of materials including: Al2O3, Fe2O3, TiO2, ZrO2, SnO2, ZnO, MgO, CuO, CeO2, V2O5, WO3, and zeolite 5A (zeolite).One un-expected difficulty (discussed below and in "Changes and Problems") was our inability to functionalized catalytic zeolites. Zeolites are common industrial catalysts for many different reactions. Our goal in aim three of this project was to functionalize zeolites with phopshonic acid SAMs in order to tune certain catalytic properties. However, all attempts to functionalize catalytic zeolites with phosphonic acid SAMs failed. We were able to form phosphonic acid self-assembled monolayers on non-catalytic zeolites, however. 2.Evaluate the performance of catalysts for dehydration of alcohols, including simple alcohols, diols, and glycerol. We had a variety of different success stories in evaluating phosphonic acid and silane functionalized metal oxide catalysts; thus, we will split this section into three categories. 2a. Trimethylsilyl functionalized gamma alumina enhances catalytic activity of diols. Gamma-alumina is a catalyst known to react simple alcohols with high activity. Reactions with diols demonstrate lower rates of reaction. After functionalizing gamma-alumina with trimethylsilyl (a silane self-assembled monolayer), we saw reaction rates of diols increase by 50%. The diol we selected was 1,2-propanediol a model compound for glycerol (glycerolhas three alcohol functionalities, while 1,2-propanediol has two, otherwise they are identical). After a series of characterization tools, we discovered that trimethylsilyl is able in increase the reaction rate of 1,2-propanediol, not by changing the reaction mechanism, which was found to be identical, but by changing how 1,2-propanediol intereacted with the surface. Temperature programmed desorption studies showed that trimethylsilyl weakened the adsorption energy of 1,2-propanediol compared with the native material. We were able to demonstrate that this weakened interaction energy could explain the enhanced dehydration rate of diols. This discovery demonstrates how silanes like trimethylsilyl can be used to tune the near-surface environment of metal oxide catalyst to enhance the catalytic properties for reactants like glycerol. 2b. Phosphonic acids of varying dipole moment are able to tune the rate of dehydration of simple alcohols. One main challenge in heterogeneous catalyst design is multi-pathway reactions, where one reactant can result in two different products. We sought to utilize phosphonic acid SAMs as tools to control multipathway catalysts, thus enhancing catalysts for a single pathway. When reacting alcohols over metal oxide catalyts, three reactions are possible, dehydration, dehydrogenation and condensation. Commerially, dehydration is the most important, in the biorefinery context, thus dehydration is a desired reaction. For example, in the gas phase reaction of 1-propanol over TiO2, ~80% of the products are from dehydrogenation, while the remaining products are from dehydration and condensation. We discovered that functionalizing TiO2 with phosphonic acid SAMs, drastically shifted the selecivity pattern, resulting in nearly ~85% dehydration product. Most interestingly, it appeared we were able to control the rate of the dehydration reaction, by changing the tail functionality of the self-assembled monolayer molecule. Surprisingly, the dipole moment of the tail functionality appeared to be an adequate descriptor for dehydration rate, the stronger the dipole moment away from the surface, the higher the dehydration rate. Through a series of experimental and computational efforts we were able to demonstrate how these SAM molecules are able to tune the rate of 1-propanol dehydration and minimize the undesired side reaction, dehydrogenation. 2c. Functionalizing TiO2, SnO2, and CeO2 with phosphonic acidsenhances dehydration of simple alcohols; all other oxides demonstrated lower rates of dehydration after functionalization with phosphonic acids. Upon discovering how SAMs improved the selectivity of reactions over TiO2 toward dehydration, we explored how broadly applicable this strategy was for other metal oxide catalysts. To our surprise, functionalization of phosphonic acid SAMs drastically lowered all reactions, dehydration, dehydrogenation and condensation on a wide variety of catalysts, except TiO2-anatase, SnO2 and CeO2. Through a study of bulk properties, we discovered these three materials share a similar, metal-oxygen bond strength, which seems to be the only similar characteristic between these materials. Thus, the discovery of controlling multi-pathway reactions of alcohols on metal oxide catalysts using phosphonic acids,appears to be unique to three catalysts: TiO2-anatase, SnO2, and CeO2. 3.Evaluate SAM-functionalized zeolite catalysts. To the best of our knowledge, there were no studies, prior to this work,that investigated functionalizingzeolitesusing phosphonic acid SAMs. In this project, we sought to functionalize variouszeolite catalysts with phosphonic acid self-assembled monolayers. Unfortunately, the zeolites typically used as catalysts couldn't be functionalized with phosphonic acid SAMs. We repeatedly tried to functionalize these catalysts and were unsuccessful (as determined by typicalcharacterization tools). This significantly hampered progress of this aim. By studying a variety of zeolites, we were able to find certain zeolites that were able to functionalized with phosphonic acid SAMs. One zeolite that we were able to routinely functionalize was Zeolite 5A. 5A is not used as a catalyst, but is used as a dessicant and in gas separations. Thus, the direction of this project changed to focus on a non-catalytic zeolite, zeolite 5A. There are significant industrial interests in 5A due to its ability to separation small molecules like carbon dioxide and n-butane. The most obvious industrial usewould be to purify natural gas streams to remove water and carbon dioxide, thus increasing the heating value of the gas. Since zeolite 5A is not catalytic, we sought to understand how phosphonic acid SAMs would modify the rate of diffusion of gases into the zeolite. Understanding the diffusion properties of these highly porous materials is difficult and insights from these studies could be utilized in the future for research groups that are able to discover a means to reliably functionalized catalytic zeolites with SAMs. Reactions with catalytic zeolites are complex and require and understanding of molecules diffusing into the zeolite, reacting on a catalytic site, and diffusing out of the zeolite. Our work here helps provide an understanding of how SAMs can tune the diffusion properties of zeolites, while excluding the complications of a simultaneous reaction. To our surprise, phosphonic acid SAMs were able to tune the rate of diffusion of gases into the zeolite as a function of the size of the phosphonic acid modifier, larger phosphonic acids had relatively small change to gas diffusion, while smaller phosphonic acid SAMs resulted in significant lowering of gas diffusion rates. Thus, phosphonic acids SAMs could be designed to provide tunable diffusion rates of gases into zeolite 5A.
Publications
- Type:
Theses/Dissertations
Status:
Accepted
Year Published:
2018
Citation:
Lucas D. Ellis, "Controlling reaction and adsorption on metal oxides with self-assembled monolayers" PhD dissertation, University of Colorado, Boulder, 2018.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2019
Citation:
Ellis, L.D., S. Parker, J. Hu, H. Funke, J.L. Falconer, J.W. Medlin. (2019) Tuning gas adsorption selectivity and diffusion rates in zeolite 5A with phosphonic acid monolayers. Submitted.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2019
Citation:
Ellis, L.D., J. B. Soberanas, D.K. Schwartz, J.W. Medlin. (2019) Effects of metal oxide surface doping with phosphonic acid monolayers on alcohol dehydration activity. Applied Catalysis A: General, Accepted.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Ellis, L.D., R.M. Trottier, C.B. Musgrave, D.K. Schwartz, J.W. Medlin. (2017) Controlling the Surface Reactivity of Titania via Electronic Tuning of Self Assembled Monolayers. ACS Catalysis, 7: 8351-8357.
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Progress 02/01/17 to 01/31/18
Outputs
Target Audience:The target audience of this work is the industrial and academic R&D community involved with biomass derived compounds (e.g. glycerol), and the further refining of these compounds into value-added products. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?I have been able to attend two national conferences in 2017, the North American Meeting on Catalysis and the American Institute of Chemical Engineers Annual meeting. I presented my work at both meetings (and acknowledged this funding source). How have the results been disseminated to communities of interest?I have been able to attend two national conferences in 2017, the North American Meeting on Catalysis and the American Institute of Chemical Engineers Annual meeting. I presented my work at both meetings (and acknowledged this funding source). This work was also published in the Journal, ACS Catalysis (see publications) What do you plan to do during the next reporting period to accomplish the goals?Research efforts to achieve the listed goals above are on going. We feel confident we will be able to address each of the aims. I also plan to attend the 2018 American Institute of Chemical Engineers conference to present my results.
Impacts
What was accomplished under these goals?
We have had great progress of utilizing Self Assembled Monolayers (SAMs) to functional metal oxide catalysts. Here is a brief progress report for the objectives listed above: We have explored the materials that can be functionalized with silane and phosphonic acid monolayers. We have been able to funtionalized a broad spectrum of metals oxide materials including: Al2O3, TiO2, ZrO2, WO3, SnO2, CeO2, ZnO, SiO2, SiO2-Al2O3, Zeolite 5A, Zeolite 13x, and SAPO34. From our preliminary results it appears phosphonic acid monolayers are capable of forming a many different oxides. We believe this to be very promising considering the wide variety of applications in which these materials are used. We have had success with two main thrusts: 1) functionalizing Al2O3 with trimethylsilyl (a silane) and 2) functionalizing TiO2 with phosphonic acid monolayers. In the first project (published in the journal Catalysis Science and Technology), trimethylsilyl was found to increased the catalytic activity of Al2O3 by a factor of two. After a thorough investigation, we determined that multifunctional alcohols, like glycerol or 1,2-propanediol, can temporarily deactivation some catalyst surfaces, like that of Al2O3, by binding strongly in a non-reactive geometry. However, upon functionalizing Al2O3 with trimethylsilyl, this non-reactive binding geometry appears to be blocked, allowing for the reactant to enter a reactive binding geometry. This work was published in the journal, Catalysis Science and Technology. We have also studied how phosphonic acid monolayers impact the dehydration activity of TiO2.TiO2 is a poor dehydration catalyst, because it also produces the dehydrogenated product in competition.However, upon functionalization with phosphonic acid monolayers, we were able to produce nearly 100% dehydration product, shutting down the dehydrogenation product.Through a series of experiments were are able to demonstrate a tunable reaction rate, by changing the dipole moment of the tail functionality of the self assembled monolayer.We were able to demonstrate that the tail functionality of the self assembled monolayer was able to shift the geometry of the transition state (of the reaction) toward a more product like geometry, in other words, the barrier of dehydration was lowered.To the best of our knowledge this is the first of it's kind study. 3) We have begun work on functionalizing zeolites with phosphonic acid monolayers. We have been able to demonstrate that these SAMs can form on several zeolites, including: SAPO-34, Zeolite 5A, and Ferrierite. This work is on going.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Controlling the Surface Reactivity of Titania via Electronic Tuning of Self-Assembled Monolayers
Lucas D. Ellis, Ryan M. Trottier, Charles B. Musgrave, Daniel K. Schwartz, and J. Will Medlin
ACS Catalysis 2017 7 (12), 8351-8357
DOI: 10.1021/acscatal.7b02789
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