Investigation of Rh-titanate (ATiO3) interactions on high-surface-area perovskites thin films prepared by atomic layer deposition

an example of application of ALD in the field of catalysis

Session Notes:


Chao Lin

Researcher at University of Pennsylvania  




Thin, ~1-nm films of CaTiO3, SrTiO3, and BaTiO3 were deposited onto MgAl2O4 by Atomic Layer Deposition (ALD) and studied as catalyst supports for Rh. Bulk ex-solution catalysts, synthesized by reduction of ATi0.98Rh0.02O3 (A=Ca, Sr, and Ba), were also examined for comparison. Scanning Transmission Electron Microcopy (STEM) and X-Ray Diffraction (XRD) demonstrated that each of the films had the perovskite structure and formed uniform coatings that remained stable upon redox cycling at 1073 K. Rh was also added by ALD and was found to interact very strongly with CaTiO3 and somewhat less strongly with SrTiO3, while Rh on BaTiO3 was similar to Rh on unmodified MgAl2O4. STEM measurements of Rh on CaTiO¬3 films showed the Rh remained well dispersed after repeated oxidations and reductions at 1073 K; however, the Rh appears not be reduced to the metallic form and was inactive for CO-oxidation reactions. Rh also interacted strongly with SrTiO3 films but could be reduced to form small metal particles that were active for CO oxidation upon reduction at 1073 K. There was no evidence for strong interactions between Rh and BaTiO3, and the reducibility and catalytic activities of the Rh/BaTiO3/MgAl2O4 were similar to that found on Rh/MgAl2O4. Evidence from CO-TPR, FTIR, and XPS all indicated that the degree of interaction between Rh and the three perovskite films can be ranked in the following order: Rh/CaTiO3/MgAl2O4 > Rh/SrTiO3/MgAl2O4 > Rh/BaTiO3/MgAl2O4. Possible explanations for why Rh on CaTiO3 films show properties that are different from Rh ex-solved from bulk CaTiO3 and why Rh interacts differently on CaTiO3, SrTiO3, and BaTiO3 are discussed.

0:00:02   Hello Everyone hope everyone stays safe and healthy during this on his battery operated on Children
0:00:08   University of Pennsylvania. Today I'll be talking about one application off. A Odeon appealed off
0:00:13   dialysis. More specifically, I'll be talking about how I prepare same proposed by poems by OD and
0:00:20   try to understand them at over respective human interactions for care.
0:00:28   The motivation for my work. ISS really. We try to attack all the real world problem off metal
0:00:33   century, especially in the field of emission control. Cater's here I'm giving is an example of prey.
0:00:40   D'Amore Lumina were initially well dispersed particle just centered and become huge ones after high
0:00:47   temperature read all cycles. And currently there is no good solution toe that, other than we put
0:00:53   more material toe that. So obviously, if we wanna make the initial standard after long term of radar
0:01:00   cycles in terms of operation, we are constantly wasting lost hope, the precious metal and the idea
0:01:09   that's into uniquely capable. So solving this problem is the concept of intelligent Cater's any
0:01:16   intelligent, cutest, just a quick introduction Here, intelligent Kathy is a method Oprah's guy that
0:01:22   has a baby all to restructure, as I'm sure in new. On the right side here, metal could be any off
0:01:27   the transition. Metal and prostate material can be something like a cousin Paquet or Strong can
0:01:33   tighten. There are many other common murals have least our baby or three structure, and the process
0:01:41   we want to utilize is really a solution process. The idea behind a solution processes that when is
0:01:48   oxidized unity optimising? Exercising the transition metal will be also ties and become metal cart
0:01:54   lions that would amend in the pros guy lattice. After reduction, these metal Karan's will be reduced,
0:02:00   become particles and then migrate to lists of this show some catalytic properties from there. The
0:02:08   year is really solving a problem because I can give you one of the example. Here are practicum, the
0:02:16   supporter on alumina and also is all from a causing tight May because see here clearly that after
0:02:24   high potential Redox cycles platinum Oromia just intern and come huge particles more than 100 on a
0:02:31   leader in diameter. Whereas if you have ah, intelligent platinum catalysts, kratom with cause I'm
0:02:38   fat may host Well, we can see here is that the platinum remain quite dispersed and the diameter the
0:02:44   size are usually around 123 not me.
0:02:49   But the concept of intelligent cater's doesn't really work, and I'll give you some reasons why there
0:02:56   some thing that we need to improve here first over its surface area. So when we are synthesizing
0:03:03   these proposed by materials, the last study is usually high temperature, constant nation, and as a
0:03:09   result, up there here, I'm showing you a tiny table complainants of this area off cause and patently
0:03:15   and Mindy's roommate, which is say, That's really your support. You can see that the first time a
0:03:20   tree of the surface area is rob broccoli 20 times door and that opera in Dutch else supply. So this
0:03:29   is not really a commercially viable, because that means if we have the same activity, we need 20
0:03:35   times higher body, and the other reason is the absolution process. In a matter particle. After it
0:03:44   formed first and then segregate to the surface, it is very hard to imagine that the form particles
0:03:51   travel across the 100 on a meter crystal and go to a surface, and I'll give you one example here
0:03:58   where this is a system of Lance Armstrong on him. Tighten it opens Niko and all these price boss
0:04:04   here, actually, nickel particles. And, uh, you can see here This is a cross sectional image only the
0:04:12   one that so called here is actually on the gas interface that is accessible to cast cast place, Free
0:04:20   agent. So even if we are utilized in a concept, we are still wasting LeSabre eyes all particles here
0:04:28   because there are embedded.
0:04:34   So here is the idea we proposed. If we can have a high surface area support material and then try to
0:04:40   code here with us in Paros vacuums And if the think archive film can have a similar party as their
0:04:47   ball counterpart, we might be able to solve a problem. But before I go into too many experiment ho
0:04:54   details let me go through a simple calculation with you and give you some idea about what exactly is
0:05:01   such as I feel thickness we want So the calculation is this the here? Very simple. We took a high
0:05:07   surface area support material and a coda with a one on a meter film assuming involved constant
0:05:13   Ternate density off 4.0 grand per centimeter cube. We end up having point for a seven grams off
0:05:19   mature deposit down onto a program of support. Let us roughly 32 way percent, really to take away
0:05:26   points from here. First is that no matter what we're growing murdering weekend acquired dramatically.
0:05:32   It would be a good way for us to keep trying on the film sickness if the film is deposit down
0:05:38   uniformly. And the second take away point, which is quite important, is that we are really limited
0:05:44   to this man who made a regime because to higher loading would just be to decrease off a specific
0:05:50   surface area, which is more desirable for us for this application.
0:05:57   So that's why we want to utilize our concept of Tom Elliott opposition here. I won't be going into
0:06:03   too many details about a tamale a deposition, because I believe most of the audience are actually
0:06:09   experts in this field. But one completely only cycles, actually more police forceps comes emotional
0:06:16   precursors for you. No, by products become removal and personal by protests again. So there really
0:06:23   to take away points year in tow. Advantages we want utilize from the atomic later position first is
0:06:29   that the grocery is usually small and less time 0.1 on a meter per cycle. If you remember, we want a
0:06:37   one nanometer perfume, so this is the worst rate is actually desirable for us. Took that to the
0:06:42   desire film segments we want and the second advantage off a odious that groceries are actually
0:06:49   similar for most of the work size, although that LD will only allow one oxide the position at the
0:06:55   time. Uncle imagine, just deposit different oxide stone as long as we control the story commentary
0:07:01   between those two. And then finally, we can heat it up and let us somewhat an every attributable a
0:07:06   design face we want.
0:07:11   So so far I have Bean focusing on preparing things, temporal sky materials and place on many off the
0:07:18   evidence I have. We believe that the box provides guy Astro in the schematic. Here is very different
0:07:24   from our air, the samples and one reason we believe that the tool the difference in a saturated
0:07:30   property. It's actually the difference in Christo size when you have a Barbara sky with the size of
0:07:37   a Roman on a meter, crystal size is no hard to imagine that metal particles can go in an hour so
0:07:44   that a solution process could actually be achievable. But now we're switching toe the film thickness
0:07:50   to around. When the one on me with the particle size off still 1 to 10 on a meter, it's very hard to
0:07:57   imagine there's a bulk for the metal toe go in. So as a result of that, we are definitely seeing
0:08:04   very different behaviour between the bulk pross guy materials and our A O D samples. So the
0:08:11   questions we are asking,
0:08:15   So the question we're really asking ourselves here is what exactly is a Trans guy support for? If we
0:08:21   have the cross SkyTeam films and what characters need to different degree or metal support
0:08:27   interactions? And if you notice on the title of my talk, I will be focusing on. It's actually on the
0:08:32   tight made for us guys. The reason behind it. It's actually if you look at a periodic table council,
0:08:40   um, strong them burial actually under the same column and all these three tightness have very
0:08:46   similar structure. We believe this is a good candidates to star with, at least to give us something
0:08:53   about the metal support interaction here.
0:08:59   So now be going into the experimental details. Hopefully By the end of this talk, I will convince
0:09:06   you that we have successfully prepared for us Kaitainen fumes and when using as a support for
0:09:13   rhodium we up there very different broken properties. And if we were to have a ranking off thes
0:09:20   materials, we could see the rhodium interest strongest with a constant Titan. 18 films followed by
0:09:27   Rodion Strong and tightening interaction and for followed by our rhodium comparing tighten me for
0:09:33   parent tightening, thinking there's pretty much no interaction between the pros guide and the metal
0:09:40   already. Okay, so now let's get started. So what I'm showing you here are two representative
0:09:49   groceries for a R D processes. Using our own home build LD set up with their precursors and also
0:09:58   Osman this day Here, you can see that both off the grocery are actually quietly near. And if we do
0:10:04   the same calculation as I show you previously, well we can see is that a calcium and titanium
0:10:10   grocery are Rafi in 2 to 3 ratio. I also this to some other air. Due process is gross right here.
0:10:17   You could see there almost all within one, or there are many to which give us ah, capability of
0:10:24   controlling That's dark, your much e. So we decided to alternate the calcium and titanium a Odeon
0:10:32   toe in a 3 to 2 minutes. As a result. Up there, I'm sure another grocery. When we mixing these two
0:10:39   LD grows together, you can see that the grocery is still quiet in here, and the after 40 cycles off
0:10:45   deposition, we are getting Ruthy Sunday hired and point program off material home to a program of
0:10:51   support, which is, if you remember from the previous calculation, roughly one on a meter off across
0:10:58   guy three times Start commentary was at reconfirmed by I c t analysis for audience for us guy
0:11:04   materials to be around 1 to 1 and depends on the cross guy density we have, Ah, very Assaidi,
0:11:12   different healthy thing. Film loading. But if we look at a film thickness, that's all around 143 my
0:11:19   heroes.
0:11:24   Okay, Now let's take a look at what the air the process will give us here. I'm showing you is I tm
0:11:31   with elementary maths and mental maps for four elements that is actually on the surface. On the left
0:11:38   side is ah d m image much. There is no much off faced operation here indicating we have good mixing.
0:11:47   If we look more carefully at the Kassam and the titanium elemental maps shown on the bottom here,
0:11:54   you can see that there is a win. Are these two materials that has actually line outside of money
0:12:01   that illuminates office? Let's imagine this week looking through day scream and the support particle
0:12:09   is actually a three D. Parker. So the fact that we have ah Bryant rain outside really suggesting
0:12:15   that we we have a good uniform coating offer materials around our s apartment two years
0:12:25   and we do have other evidence for good coverage, which is pro by a reaction technique temperature
0:12:32   program. Dis option. What I'm doing here is as a partner in dehydration reaction. So I support my
0:12:38   dehydration. Is mom to be related to a selfless acidity? So here, for example, for Melissa roommate,
0:12:45   which is a very strong Lewis, as it we can see here is that when we are increasing the temperature,
0:12:52   no, we act him being almost all reacted to become products protein and even a surface at the
0:12:59   temperature over for 70 Calvin. And if we have and that is a very typical Lewis as a behavior where
0:13:08   Malaysia illuminates a strong recesses. So the temperature for the reaction to happen is relatively
0:13:13   low. But now, if we have a prospecting film coating the behavior a totally different as shown by
0:13:20   these three TPD process on the right side here you can see that for all of this, the peace are
0:13:26   actually shifted toe a higher temperature. Well, I want to emphasize here is that there is no peak
0:13:33   at 4 70 could be pumped indicating there is no bear Molina room they on the surface again. This is
0:13:40   really indicating we have a good coverage often materials by our a All these in films
0:13:51   So remember we really wanted for all sky fees, but not just random oxides now. And we really
0:13:57   achieved there as strong by the ex i. D. Pattern here. So why I'm from your here is four x adi
0:14:05   patterns Behrman in a loony and three men in a room named modify with across one day impressed kind
0:14:11   materials. We can see that after high temperature consternation, the on the new peaks that showed up
0:14:19   actually cost around into the on first time materials. There's no other P could be found indicating
0:14:26   that we are really having a good, uh mixing and we are forming that entire face. We want the cross
0:14:34   that place surface area also compared and included here. Oh no, we are separates rising a little bit
0:14:42   because we're putting a tense fumes down. You can see that the three Metiers definitely have a much
0:14:47   higher subjects. They're comparing toe their power counterparts
0:14:55   so hopefully so far at convincing that we are able toe May uniforms for all SkyTeam film with a few
0:15:02   ticks myself around one on a meter and we have that desire face we want. Now I'll be adding road
0:15:08   into these for disguising film surface to investigate the interaction between rhodium and the
0:15:14   prospect materials. The first day that really draw our attention is we observed very different road
0:15:20   and geometries found from the TM images. If we are putting rodent down onto a constant type native T
0:15:27   on supports, what we're seeing is that after had time to read all cycles with a final treatment
0:15:33   being reduction, we cannot see any off the rule of the and particles at all. And from the TDs maps
0:15:41   here, we can see the rodent remain well dispersed on the support surface. This is really not common.
0:15:49   And we are no observing this on any other zapor materials. If we have Ah, a rhodium on strong team
0:15:58   Titan Lee. Well, we ends are happy. I don't know if a resolution is going up here, but you can see
0:16:04   all these tiny price parts that are actually rhodium particles. Eso rhodium on strong can't happen.
0:16:12   I definitely have a very different geometry without small particles. Is this thing on the surface
0:16:20   Roughly around 1 to 200 meter inside. If we're looking at rhodium on very tight in aid, geometry is
0:16:28   again different. So all these huge bright dots I actually now the road and particles. We are
0:16:35   observing a much larger roading particles with a diameter over on 1 to 10 centimeters in size
0:16:44   and are finding from TM images are surgery confirmed by the empty I R. So what I'm doing here is pre
0:16:52   reduce assigned poppers and try to introduce CEO to a sample surface to see where the assault from
0:16:59   frequency will be at. And if you are looking at rhodium on concept tightening as I'm showing on the
0:17:05   map here. There's no CEO comes option could be found really indicating that rhodium might be
0:17:11   remained in the lattice or that is now on the surface. Or it could also be awesome sized. But if
0:17:18   we're looking at our rhodium on strong team, tighten that you can see these two peaks and the like.
0:17:24   The representative for the company information now would usually only before on various more rhodium
0:17:31   clusters or rhodium single Adams on That confirms our finding from the TM image, where particle size
0:17:38   are around 12 to 1 on a meter for rhodium on barren tightly. What we're seeing is that Onley, the
0:17:45   representative p for denia, or bridge impound could be on the FBI are pattern and that really
0:17:52   corresponds to a lot of rolled in particles. So again match up nicely with our tea on finding.
0:18:03   So hopefully so far I convinced you that the interaction or rhodium thes three for US government,
0:18:09   your very different and that will also d to ah, very different growth and geometry. But when we care
0:18:16   more about is actually the rhodium support international, what would be the result in are calculated
0:18:23   performance So what? I am prodding here after the Iranians product for our probe reaction. See ya.
0:18:30   Sedation foreignness. Probably a prodding is a race as a function off south and nobody so the right
0:18:38   hand side of the problem in higher activity. So here are implanting is the rhodium activity as a
0:18:45   function off pre treatment condition, pre reduction temperature So we can see that for rhodium on
0:18:51   Qassam tightly, no matter how harsh we reduce it actively remain quite low compared toa the order to
0:18:58   sample. So just in voting might be remaining that that us or its are being covered by something that
0:19:06   is leading to inactive brilliant performance before rhodium on strong team Titan E. We can clearly
0:19:13   see a jumping activity after low temperature reduction and another john up the high temperature
0:19:20   reduction. Very typical rhodium behavior will have us drone interaction with the support in the
0:19:26   behavior actually very similar to about a solution. The findings so suggesting some degree of
0:19:33   interaction between rhodium and that strong him tighten anything feelings. But if we now look at
0:19:38   Rhodia Mulberry in tight may, a mild reduction at 300 sauces or by 73 K is enough to reduce a sample
0:19:47   and have very high activity. This is a good indication off there is, ah, week international even
0:19:54   know interaction between rhodium and a different type of game films.
0:20:01   So we really want to try toe, have ah quantification or semi contact education off the road and
0:20:08   support interaction, and that could be actually pro by temperature program reduction for a
0:20:14   temperature program reduction here. Where we are parting is the amount of co two produced a CEO to a
0:20:21   signal when you since U S A re agent as a function off the temperature. So what we're seeing is that
0:20:28   if you have ah, very weak in the Russian between rhodium and you can see the peak center at lower
0:20:36   and 600 k So he had a proud the lower temperature leaves. The easier it is to reduce a rodent means
0:20:44   that we could interaction and we can see that war rhodium moment either on roommate and the running
0:20:51   on Baron Tight. Nate, we are both during Is the temperature peak so dressed in weak interaction
0:20:57   between rhodium and the corresponding support materials for a strong team Titan A. We are seeing
0:21:03   some ship towards higher temperature and this is a continuous bombs. So that was suggest we have
0:21:11   different interactions and definitely much stronger confirmed to A or D shown here for rhodium on
0:21:20   cousin Tighten, a national that actually shows very strong the strongest interaction among audience
0:21:26   samples. We can only see a tiny problem here until hired at 700 Calvin and the area, if you were
0:21:36   actually corresponds to the amount of reduction that is actually happening. The area for the record
0:21:42   is relatively small compared to the others, suggesting rodent might not be fully reduce in this
0:21:49   reaction environment.
0:21:55   Okay, so that will come to the end of my talk here. Hopefully I've convinced you that off course, we
0:22:01   prepare high surface area for a SkyTeam feel that our uniforms and we have Chris corresponding for
0:22:08   us guys structurally will. And if we are put in road in town, we definitely observed different
0:22:14   degree off interactions, and that interaction can be to a different rhodium geometries. If we were
0:22:20   to have a ranking off, the degree of interaction will be following order. Well, they're interested
0:22:27   youngest with cost them tightly their kills followed by the interaction between rhodium and the
0:22:32   strong and tight mating films for parent tightly supporting on my leader. Arguably, there is almost
0:22:37   no interaction could be up, sir, when as a support for rhodium caches
0:22:45   with honest, I like to think my P I also grew members from Gotti and those group, and I also like to
0:22:53   thank the funding source for financial support, and I will be open for questions if you have any,
0:23:00   thank you.