Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum 

Session Notes:


Qing Peng

University of Alabama




Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones owing to their larger specific surface areas of desirable crystal facets. However, often, these SENs are less stable because the desirable surface facets have higher specific surface energies than other types of facets. Therefore, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures to achieve favorable kinetics. In this paper, we show that atomic layer deposition of Al2O3 can modify the shape-engineered CeO2 nanorods (NRs) to not only increase their shape transition temperature from 400 ºC to at least 700 ºC, but also greatly increase their reversible specific oxygen storage capacity (srOSCupto 700 ºC. Through Al2O3 atomic layer deposition at 200 ºC, trimethyl aluminum reduces the Ce4+ to Ce3+ and substitutes Ce3+ ions with Al3+ to form -Al-O-Ce-O- structure. The substituted Al3+ ions impede the surface diffusion of Ce ions, therefore improve the thermal stability of CeO2 NRs. The Ce ion in -Al-O-Ce-O-, a new Ce species, can be reversibly reduced and oxidized at 500 – 700 ºC. Our method presents a new strategy to improve the thermal stability and catalytic activities of SENs, thereby expand their applications into high temperature environments.

0:00:09   Hello, everyone. This is Qing Peng from the University of Alabama. Today. The topic of my
0:00:19   presentation is above sensor sizing stable on the catalytic lee active shape engineer serum oxide.
0:00:28   And then all, by controlling doping off aluminum can rise. This work is many being carried by coming
0:00:40   in, don't you? She's so young, Onda, Some other old other coursers,
0:00:55   the continent off my presentation today is least here. So we will talk about the background off
0:01:03   serum oxide on these serum oxide the matter offs. And we're gonna talk about why we want to use air
0:01:09   D to stabilize serum Ox. I I don't talk about our Messer, either. Gonna shit. Then we will show is
0:01:17   you the experiment results and our discussion of this results, and we're gonna talk about it
0:01:24   conclusions. And finally, we're gonna conclude with local management.
0:01:31   So
0:01:34   by ground of serum oxide, serum oxide is a generally can be organized into crystal structure like
0:01:41   this, and serum outside basically is a started. They can supply and store auction, for instance, the
0:01:52   reason serum oxide can supply and the stool auction. It's because serum kemayan can switch between
0:01:59   three plus and a four plus for instance, in 40 all sides of serum oxide. If we supply reducing agent
0:02:08   like like caramel oxide, this cover monoxide will be oxidized into CEO too. By taking auction from
0:02:16   the serum oxide
0:02:19   on the other side, it reduced the serum outside. Basically, serums three plus can be oxidized by our
0:02:27   station agent, for example. Oxidizing agent, for example, option to producing staring props 74 plus.
0:02:38   Therefore, we see that serum oxide is a is a sorry they can supply and a store auction.
0:02:47   So basically, now we understand serum outside is a relay to store on a supply auction for catalytic
0:02:54   reactions. Based on this unique properties of serum out sign, it has being widely used it as a
0:03:03   catalyst or catalyst. The support being catalytic converters, solo waters bleeding. Sorry, oxide. A
0:03:11   few sales, for instance, The most important applications off serum outside is as a catalyst support
0:03:20   being catalytic abode. In this case, serum outside is used as a support to support precious metal.
0:03:30   Have you seen it in the cavity converter serum outside? We are store on a release auction depends on
0:03:38   the scenario depends on the reaction conditions. So that's why serum outside is so important. So
0:03:48   here's brief story that off the field off the serum oxide in 19 eighties serum oxide is explored at
0:03:56   auction carriers for catalytic a voter. But people find that serum oxide itself as a pool, so most
0:04:04   ability, and then people did a lot of researchers and then find hope. Serum oxide macro particles
0:04:11   actually has, um, compromise the stability on activity so they can be used in community Kuroda. But
0:04:22   a sense they are very large party, cause they are option Keira capability actually is pretty low on
0:04:28   the need. A very high temperature to activate those options. So then people starting to explore can
0:04:34   we use serum ox and the nano materials, um, to had to enable low temperature surface reduce ability.
0:04:45   The reason is the auction on the surface can be reduced at a lower temperature than the option in
0:04:52   the bark off the serum outside, for instance, most of the surface auction can be reduced at a 400
0:04:58   see below. However, I always though serum oxide that can't see from outside the manor rose can be
0:05:06   reduced at a 400 degrees C,
0:05:10   most of them barker auction in the ceremonies and matter. Rob still cannot be extracted, and
0:05:18   everyone extract the park auction instead remarks and man rods. Then we have to go higher
0:05:24   temperature. But unfortunately, when we go high temperature stare monks and natural starting to be
0:05:31   for me not to limit their commercial on occasion. So this slides basic issues that would wanted of
0:05:38   Sarah Marks and then enter all we can see that serum outside the matter. All this shows up here the
0:05:45   balloon, any shows for the seal oxidation? Basically, they have a lower taking off temperature, Onda
0:05:54   uh, then the man, a cube and an octahedron. So that's as a benefit of the serum marks and an Iraq
0:06:04   compared to the odds of standing rock side. And here, however serum outside, like we just said, they
0:06:12   have poor, so much stability sear marks and that Iran's has a beautiful broad shape. Look. If you
0:06:20   hit them up at 700 degrees C for five hours in nitrogen auction environment, they will be converted
0:06:27   into serum oxide. Nanoparticles lose their shape. The reason is because that matter, Rob has surface,
0:06:37   Post said. That High has high energy, and the Nana Rocks has higher circus era program on their
0:06:44   stomach. Dynamically, this material would like to become war into spears. On the way is more stable,
0:06:51   less active super sites. So how do we stop this parcel as we know that we want to use their muscle
0:06:59   in general because they have only wanted they have low temperature auction activity, oxygen
0:07:05   activation. You have a highest of surface auction program, Simoes. But the challenges We cannot
0:07:12   extract the Parker auction which you need 500 steel ball. I'm Sarah outside minerals only stable up
0:07:20   to 450 degrees C on it needs 450. However, when temperature higher than the 400 degrees. I wonder if
0:07:30   you did You receive that Iran's were changed their shape and then lose the auction capacity.
0:07:38   So how do we solve this problem? So we think about that. Why can't we, you know, add a little bit
0:07:46   more so more stable more somebody stable materials, for example, aluminum oxide onto the surface to
0:07:53   stabilize the serum oxide because at the end, the information off the serum oaks and men around is
0:08:00   because of the movement off of the ceremony. I'll So this lies basically summarized, was a comically
0:08:10   of the position on the used try Miss Aluminum and the water as the core reactors for the older mark
0:08:15   side deprivation. So we all know that if the service has a perfect Ohh, there's a West Group. We
0:08:22   will get a nice model layer by modeler accumulations. Generally, basically, in reality is summer.
0:08:28   Monterey accumulations. You gotta one instrument or cycle or from outside of gross. So Air D has
0:08:36   been used to stabilize ox too stable to stabilize nanoparticles. And there's many serious cover
0:08:44   scenery said that motivated our study. Is that over coating, um, conformers over coating on the
0:08:52   conformers recruiting, then followed by cranking. And then our hypothesis is that air D could form
0:08:59   serum oxide own months at a kosher structure on the aluminum oxide. If the Oldham outside show is so
0:09:06   fine, that auction can diffuse serum outside, maybe becomes so many stable on the auction, still
0:09:14   can't refusing you out. So that's our message. So we basically take the serum outside. The matter
0:09:21   all spread them into cause tube, and then we expose them to a regular room outside. We expect to
0:09:27   form on the outside of shell on, then encapsulate the most serum oaks and that a rolls. So Sarah
0:09:34   marks and minerals is since aside about hydro, some a method on the condition is shown here. So
0:09:41   basically is no temperature process below 100 degrees C on the air. The condition we use we we load
0:09:51   the serum outside minerals, and they keep this. Now, keep this sample at 200 degrees C. Imagine for
0:09:58   more than 730 degree C two to remove, um, moisture, and then we expose it to tear me in the water or
0:10:08   collectively. And then the whole experiment most of the time Istan at 200 degrees C, if not mation
0:10:16   otherwise so here is our experiment result and discussion. So, first of all, what we observe is that
0:10:25   the ha Jin comes up. So first of all, what we started it is the optional storage capacity off pew
0:10:32   staring outside at all. So this is option. This is 100 and consumption. Um, curve. So the area on
0:10:40   the niece the curve means that, um, more hydrogen is being consumed, then means that there's a more
0:10:48   auction is available from the serum oxide at that particular temperature. One. Okay, that let's look
0:10:55   at the stair marks and matter out the 1st 2 tp our window temperature program the reduction of
0:11:01   hydrogen. So you basically wrapping up the temperature while you're full of hydrogen And now you
0:11:06   hydrogen being called soup, you'll see that the taking off temperature is around 300 degrees C and
0:11:11   they have a giant peak. And then the people reduced dramatically at 500 degrees c and then of the
0:11:19   reduced it to a point and this side into taking up. Okay, on the first, a peak is the surface
0:11:25   auction. Hey, that that that hydrogen consumption is from the surface auction on the serum ox and
0:11:32   general, and then this still mustn't on. Then the second peak is from the option in the bark off the
0:11:41   serum ups and narrow, and then the and then you can see that put the state remarks and then a wrong.
0:11:49   There's a giant, um, service auction comes in concentration Monday after the first of cycle TP are
0:11:57   with did the second cycle GPO. So you can see that most on the serum outside of surface auction is
0:12:05   gone, and then the the barker ocean reduction temperature also goes to the higher temperature level,
0:12:14   by the way, the second peak yes, from the bark of ocean. And you can see that after the first of
0:12:21   cycle TV out the second cycle TP I shows that the sample has very small amount of service option on
0:12:27   the the bark. Ocean extraction actually moves to high temperature on a similar phenomena observed.
0:12:34   Even the serum marks and emeralds has to be heated up before the first TV. Outside the heat. It
0:12:40   often means the heat treatment on 700 degrees C five hours eating air so most of the surface option
0:12:47   has bean removed surface auction capacity of speaking. So what's going on? The reason is that the
0:12:54   serum oxygen that around has been deformed into surmounts atmosphere that Nana Sphere do not have
0:13:02   service auction storage, storage capability. The reason is high temperature convert this serum
0:13:10   outside man around to serum out sci fi on the serum. Outside sphere actually is highly crystal
0:13:17   actually still outside. Letter out is highly questioning as well. So then we did 45 cycles on a
0:13:24   mountainside de onto the serum ups and that around unless they that it was happens for they'll
0:13:30   auction hydrogen consumption capability, for instance, than we including that the first several
0:13:39   months and then all the first a teepee on cycle as a reference, How did you can see that the first a
0:13:44   peak is from service option on the six and Peak is from the bark option, but you can see that the
0:13:50   for the serum oaks and then Iran's was 45 cycle air be the first. The TP are they have lose some
0:13:58   surface auction capacity, but you know what? They also have more. But different type of auction
0:14:04   species has been generated that it can be reduced from 482 650 if you consider that the auction and
0:14:17   the auction capacity for reduction before 700 degrees C. Actually, the sample has been treated with
0:14:24   45. Cycle charity is much bigger than the pew, um, serum ox and that are on. You're in the first, a
0:14:31   TV outside. What is more interesting is that this air Detroit example actually is much more stable
0:14:40   on then you can slack with them packing. Enforced during the tibia urine, the ones of pence DPR
0:14:46   cycles their actions. Their auction story auction storage capacity does not change much, actually.
0:14:53   Is we bigger than the ceremonies and laterals up that high temperature treatment? So it means that
0:15:04   40 cycles 40 site, 45 cycles. Total marks at air get actually improve the stability of serum outside
0:15:10   the natural. So what's happened? So basically, what we show is that you know, 45 cycle air de
0:15:18   treatments does not change the morphology off the lateral on. We cannot see it clearly about the on
0:15:25   more force coding off the remarks that, in this case, in this loan resolution of TM But we most of
0:15:31   the more significantly this slide shows that after high turn, put your treatments 700 degrees C. The
0:15:40   manner rod shape is meant pain and that are on the shape these men time I did. That's probably the
0:15:47   reason that the surface auction species is not being totally destroyed.
0:15:55   So then what was the effect off the air? The cycle on the auction stories off the serum marks and
0:16:00   then around. So basically we can see that 45 cycles after high temper treatment is lenses incites
0:16:09   the air de of the high temperature. Treatment is like this one cycle air de of the high treatment
0:16:15   temperature treatment is like this when you can see that, um, the air dislike with definite has has
0:16:22   as a big impact on the auction storage capacity. But half the pen cycles that increasing is not that
0:16:31   dramatic is not that dramatic. You can see that this even pen cycles actually aired. The treatment
0:16:39   can dramatically improve the stability, the so much stability of the auction storage capacity off
0:16:46   the serum oxide matter, all so on. You can see that the news option species has been generated even
0:16:55   of the 10 cycles. So under these actual storage capacity, is we bigger than that? Long Children that
0:17:03   are odds in the second cycle TP are on the lung treated and around after high temperature. So that
0:17:09   is we be so that means the stability off the stage remarks and lateral is dramatically improved. So,
0:17:15   Sara So this slides basically summarized off the morphology changes off the different Air B cycles
0:17:22   and after the high temperature treatment on the sea, remarks and neurons after high temp treatment,
0:17:28   morphology totally changed on the 45 cycles. Air dear Amount side After high temperature treatment,
0:17:34   there's now changed to serum outside than around my college and after one cycle, actually some of
0:17:42   the stair amongst and that Iraq has been changed. The intern atmosphere after 10 cycles most of the
0:17:48   general has meant tended their natural shape. That's probably the reason that most off the auction
0:17:56   storage capacity, the surface auction storage capacity offer the serum ups and that Iraq has bean
0:18:02   presumed when we preserved when we carry more, a king cycle more or room outside cycles. So here we
0:18:12   want to use high resolution tm to show that the what's going on for the serum marks and that Arab's
0:18:17   with 45 cycle air decoding because we didn't see clearly the sickness off the air, decoding in the
0:18:24   previous roll resolution tear. So what you see is that the serum ox and laterals have to censor size.
0:18:30   Basic off, the sensor says, basically is highly crystalline.
0:18:35   On the 45 site 45 cycles Air D or remarks. I actually, we did not see a dramatic amount of steak or
0:18:43   maybe five centimeter. I'm office room outside, each slide over the natural. That's actually
0:18:49   surprised. So which means that you know the aluminum oxide is not a nuclear at a normal way as what
0:18:57   we expected under on the surface that has a heavy pump has a there's populated hydroxide group. So
0:19:07   what's going so we don't know you. So So the question is, is there a olo is the aluminum on the
0:19:13   surface It right. So then we did E Dax. We show that aluminum concentration there are elements, but
0:19:20   aluminum distribution is many under surface and the concentrations in low concentrations in low. So
0:19:26   we think that what happens is that, um our hypothesis is that the T M A basically goes on to the
0:19:36   surface and then reacted with option on the ceremonies and then around, um, basically acting as a
0:19:44   reducing agent, the trimester aluminum on the auction because they will be generated because, um,
0:19:51   some say that the message readings burn off, and then aluminum was substituted. The serum a car
0:19:59   tires, uh, in the serum oxide. So that's probably the reaction we can is. So why do we see that
0:20:07   we're gonna provide a boy? It is for that conclusion. So, first of all, what we show is how did they
0:20:13   are all aluminum's on the surface? As we show here after 45 cycles with definitely say that there
0:20:21   are limits Aluminum to pee peaks. We do have aluminum even though we do not have a very sick 45
0:20:28   cycles. Ah, five centimeters over months on this XPS data actually also indicate that the aluminum
0:20:37   courage actually is very thing. Otherwise, we're probably going to see a very small amount of serum
0:20:42   a serum after Cody trip. But you can see that this serum constant the serum intensity He's not
0:20:49   change much. So there we did a bto arise off x by using XPS off the on serums three plants and a
0:21:00   serum four pass on This figure is from the pew serum outside. As you can see that you see motor the
0:21:08   serums three plus related to serum four plus, that concentration actually is is a low compared after
0:21:19   you treat them with the 45 cycle Newmark site you can see obviously and now you're serum outside
0:21:25   sleep three past speakers more obviously than this serum three plus And here there's amount along
0:21:31   serum street past. So we say that the try mess aluminum probably reduced the serums reprocessed to
0:21:39   serums three full price to see import three paths in addition. What we see is that the pew sitter
0:21:46   marks on that around. Actually, the cover off Pusey remarks unnatural has been changed after the
0:21:53   treatment off the tm of the trimester. This kind of change Also indication indicating that there's a
0:22:00   more serum three plus in the in the particle. So that's one of the evidence. The second evidence is
0:22:09   that what we show it, we show, is by XPS that backs RB. What fun is that? That crystal lattice
0:22:17   actually changes after we did aluminum oxide on there on the serum oxide. As you can see that the
0:22:25   serum outside is a read on this blue. How do you see that at the peak is shifted a little bit and
0:22:31   it's indicating that a luminous three passes open into it into the structures so that the U two
0:22:39   Seita was moving to the larger number but flew into the magic number. So then we did some control
0:22:47   experiment. What we show is that we now we're not do air de cycles. We just do the trimester
0:22:54   aluminum treatment. We say that we see similar shifting off the off the crystal lattice. So what
0:23:03   does that mean? It means that the aluminum, just by trick. Just treating the serum outside with Try
0:23:10   Miss Aluminum. The the latticed constant off the serum outside were changed. That means this the
0:23:17   problem. We're substitute the syrup, um, in the serum particles. Actually, in the previous
0:23:25   literatures, doping has been used to improve the option storage capacity on the stably off the serum
0:23:32   outside. So in this case, that is serum zirconium oxide. As you can see, that stopped with zirconium
0:23:40   oxide after hey, after he treatment. As you know, not 100 degrees C. The low temperature auction
0:23:48   species has been activated, and in our case, our low temperature function species is activated. You
0:23:56   know, that's you do not need to hit them up and up to 900 degrees C. Just there you can get up to,
0:24:03   you know, and 200 diversity will have the smell temperature, um, ocean species, uh, social species
0:24:11   on then, as you can see that, um, the fresh serum outside. Actually, during the cycle, zero lose
0:24:19   their auction, the function storage capacity. So this also shows that the trimester aluminum does a
0:24:25   reactor with syria marks and arrows on a joke. Aluminum. I have cat eyes into the serum outside, so
0:24:34   effects. So that way study Oscar ourselves. So, um, what would happen if we if we can form a stick,
0:24:42   shares off the aluminum oxide onto the serum oxide we are The same phenomena shows up well that the
0:24:52   heating were former crack on the wrong side to generate, um, actual storage capacity. And then what
0:24:59   we did is we tried 45 cycles Air B on 200 degrees C on at 75 degrees at 200 degrees C. We do not see
0:25:08   much amorphous coding, but at 75 degrees C, we see a nice five spot. I'm not a meter. Um, a room
0:25:16   outside codings around the state remarks Asher Done. What we see is after high temperature
0:25:23   treatments, we do not see that low temperature auction storage capacity came up. So what does that
0:25:31   mean? That is the section of aluminum oxide cannot be correct by the serum. Oxana me You heat it up
0:25:40   to high temperature and to release the option storage capacity. So that means the mechanism is not,
0:25:48   ah, sick coding for the better cracking. So that means the mechanism is probably what what we have
0:25:56   hotter size is basically a looming trimester aluminum reduced, um, serum. The serum can I am from
0:26:04   four prosthesis repress and a substitute. Some serum can I am and then from a dope aluminum serum
0:26:12   oxide. So then why 45 cycle remarks at a 200 c cannot for five nana machine on the serum outside the
0:26:23   men reason years and the serum oxide. When you heat it up to 200 degrees C in vacuum, they will lose
0:26:30   most of the surface hydroxide group, as shown by this report. So that means when the TME goes onto
0:26:38   the surface, there will not be able to find a wedge to reactivate. They will react with the auction,
0:26:44   uh, in the serum oxide. So basically the serum out so that we oxidize the try mess aluminum. But
0:26:51   they and then that in the following cycles of air b, the reaction just the reaction religion become
0:26:58   so slow. So the conclusion after this, um, the study is at 200 c. Try mess. Aluminum can reduce. I'm
0:27:09   serums four plus two serum sweet problems and create auction. We concede, because some option is
0:27:15   reactor with is messy group and then aluminum were substitute serum irons on substitution, We are
0:27:25   form a doping. The former doping on the degree of a substitution actually is controlled by the
0:27:32   exposure time off TME. Basically Also, you can say that it can controlled by the cycle off harmony
0:27:38   cycles, exposure TME right. The so much stability on auction storage capacity of serum outside is
0:27:45   enhanced by the aluminum mystery Serene, crossed open. So that means our original hypothesis the
0:27:52   course, your structure on the stole thing. It does not work. So basically was works. Is that the
0:27:59   unique reactions between TM A and serum outside, Sir Monster. Finally, I want to, but we want to a
0:28:09   college funding source, um, A C s patron research fund and the National Science Foundation and the
0:28:15   Department of Energy. The end of the like to thank you for your attention on the I can take any
0:28:24   questions from you guys. Thank you