Mullite

There’s a tendency for folks to think of “catalyst” as being a precious metal. this is largely because platinum was (and still is) one of the best catalysts around for a lot of reactions, and folks have heard of it.

The original catalytic converters had a load of platinum in them (in some cases on the order of $1000 worth) and for a while there was a thriving business in stealing them from cars and “recycling” the platinum.

Then folks found ways to reduce the cost. Other metals were used (things like palladium) and some oxides were found that worked. Now a cat converter costs on the order of $100 and theft is less of an issue.

So what’s a “mullite” and why mention it? It’s a mineral, and a catalyst. Some folks have heard of “molecular sieves” or other forms of mineral catalysts (like zeolites), but few have heard of mullite. I ran across it while looking into ceramics and ancient pottery. Turns out some ancient Germans had a way of making fine high temperature crucibles that depended on mullite formation during fabrication. That was kept a secret for a very long time…

The Wiki has a few bits on that:

Mullite or porcelainite is a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge balancing cations present. As a result, there are three different Al sites: two distorted tetrahedral sites and one octahedral.

Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Sithean Sluaigh, Scotland.
[…]
Mullite is present in the form of needles in porcelain.

It is produced during various melting and firing processes, and is used as a refractory material, due to its high melting point of 1840°C.

In 2006 researchers at University College London and Cardiff University discovered that potters in the Hesse region of Germany since the late Middle Ages had used mullite in the manufacture of a type of crucible (known as Hessian crucibles), that were renowned for enabling alchemists to heat their crucibles to very high temperatures.

The formula for making it (using kaolinitic clay and then firing it at temperatures above 1100 °C) was kept a closely guarded secret.

So why mention it now? Aside from mineral catalysts being one of my favorite things, it has found a new use as a NOx catalyst in Diesel engines (another of my favorite things…)

tp://phys.org/news/2012-08-diesel-exhaust-platinum.html

Yes, this is from back in 2012, so not “new news”, but still interesting to me as I just found it in 2014 (yes, I’ve had this “in queue” that long). That article has a nice picture of how the catalysis happens on the stepped edges of the crystals. IMHO that kind of fine tuning where and how reactions happen will be very important for catalysts, materials science in general, and potentially for Cold Fusion / LENR process.

In a study published in the August 17 issue of Science, researchers found that when a manmade version of the oxide mullite replaces platinum, pollution is up to 45 percent lower than with platinum catalysts.

“Many pollution control and renewable-energy applications require precious metals that are limited – there isn’t enough platinum to supply the millions and millions of automobiles driven in the world,” said Dr. Kyeongjae “K.J.” Cho, professor of materials science and engineering and physics at UT Dallas and a senior author of study. “Mullite is not only easier to produce than platinum, but also better at reducing pollution in diesel engines.”
[…]
In 2003, Cho became a co-founder and lead scientist at Nanostellar, a company created to find catalysts through a material design that would replace platinum in reducing diesel exhaust (Carbon monoxide, or CO, and NOx pollutants). His company has designed and commercialized a platinum-gold alloy catalyst that is a viable alternative to platinum alone, but until this experiment with mullite, had not found a catalyst made of materials that are less expensive to produce.

Cho, also a visiting professor at Seoul National University in South Korea, and his team suspected that the oxygen-based composition of mullite, originally found off the Isle of Mull in Scotland, might prove to be a suitable alternative. His team synthesized mullite and used advanced computer modeling techniques to analyze how different forms of the mineral interacted with oxygen and NOx. After computer modeling confirmed the efficiency of mullite to consume NOx, researchers used the oxide catalyst to replace platinum in diesel engine experiments.

“Our goal to move completely away from precious metals and replace them with oxides that can be seen commonly in the environment has been achieved,” Dr. Cho said. “We’ve found new possibilities to create renewable, clean energy technology by designing new functional materials without being limited by the supply of precious metals.”
The mullite alternative is being commercialized under the trademark name Noxicat. Dr. Cho and his team will also explore other applications for mullite, such as fuel cells.

More here:

http://www.sciencemag.org/content/337/6096/832.short

Mixed-Phase Oxide Catalyst Based on Mn-Mullite (Sm, Gd)Mn2O5 for NO Oxidation in Diesel Exhaust

Weichao Wang1,*,†, Geoffrey McCool1,†, Neeti Kapur1, Guang Yuan1, Bin Shan1,2, Matt Nguyen1, Uschi M. Graham3, Burtron H. Davis3, Gary Jacobs3, Kyeongjae Cho1,4,5,*, Xianghong (Kelly) Hao1,*
+ Author Affiliations

1 Nanostellar Inc., 3696 Haven Avenue, Redwood City, CA94063, USA.

2 State Key Laboratory of Materials Processing and Die and Mould Technology and School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China.

3 Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511, USA.

4 Department of Materials Science and Engineering and Department of Physics, University of Texas at Dallas, Richardson, TX 75080, USA.

5 WCU Multiscale Mechanical Design Division, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Republic of Korea.

↵*To whom correspondence should be addressed. E-mail: wwang@nanostellar.com (W.W.); kjcho@utdallas.edu (K.C.); xhao@nanostellar.com (X.H.)
↵† These authors contributed equally to this work.

ABSTRACT
Oxidation of nitric oxide (NO) for subsequent efficient reduction in selective catalytic reduction or lean NOx trap devices continues to be a challenge in diesel engines because of the low efficiency and high cost of the currently used platinum (Pt)–based catalysts. We show that mixed-phase oxide materials based on Mn-mullite (Sm, Gd)Mn2O5 are an efficient substitute for the current commercial Pt-based catalysts. Under laboratory-simulated diesel exhaust conditions, this mixed-phase oxide material was superior to Pt in terms of cost, thermal durability, and catalytic activity for NO oxidation. This oxide material is active at temperatures as low as 120°C with conversion maxima of ~45% higher than that achieved with Pt. Density functional theory and diffuse reflectance infrared Fourier transform spectroscopy provide insights into the NO-to-NO2 reaction mechanism on catalytically active Mn-Mn sites via the intermediate nitrate species.

It also looks like a related material with Rh instead has promise for use in rockets as a N2O propellant catalyst:

http://pubs.rsc.org/en/content/articlelanding/2010/cc10.1039/b925085a#!divAbstract

A mullite-supported Rh catalyst with an unusual crystalline structure in favour of high-temperature reactions was applied for the first time to the catalytic decomposition of N2O propellants, and has shown a promising initial activity and thermal stability.

Interesting stuff these mineral catalysts…

Over time this will put considerable pressure on precious metal catalysts. Since it looks like this process “generalises” and can be modified / tailored, expect to see it spreading into other uses of platinum catalysts.

Perhaps that explains why this platinum ETF has been almost cut in half since 2011 …

PPLT Platinum ETF 10 year chart 17 April 2015

PPLT Platinum ETF 10 year chart 17 April 2015

(Though, in fairness, GLD and SLV had higher peaks and also have been downhill since about the same time…)

In a quasi-related “no limits on growth” link from that first phys.org article was one about batteries. In particular, a lot of folks have their panties in a bunch about lithium scarcity ( even though you can use potasium instead…) So here a bright guy has figured out how to make a similar battery with magnesium:

http://phys.org/news/2015-04-lithium-iona-significant-battery.html#inlRlv

Researchers at the University of Illinois at Chicago have taken a significant step toward the development of a battery that could outperform the lithium-ion technology used in electric cars such as the Chevy Volt.

They have shown they can replace the lithium ions, each of which carries a single positive charge, with magnesium ions, which have a plus-two charge, in battery-like chemical reactions, using an electrode with a structure like those in many of today’s devices.
[…]
Having established that magnesium can be reversibly inserted into electrode material’s structure brings us one step closer to a prototype, said Cabana.
“It’s not a battery yet, it’s piece of a battery, but with the same reaction you would find in the final device,” said Cabana.

Simply put, the “magic” in the lithium ion battery is not the lithium, it is the non-metal matrix into which the ions are pushed. Lots of ions will work, lithium is just a very light one. With 2 charges per ion, magnesium lowers that advantage / mass.

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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7 Responses to Mullite

  1. Ian W says:

    The next battery technology though could easily be Aluminum based see http://news.stanford.edu/news/2015/march/aluminum-ion-battery-033115.html
    I have no doubt there is more to dig into behind this press release.

  2. E.M.Smith says:

    @Ian W:

    IF they can do what they claim, that’s quite a battery.

    I suspect that despite all the things folks have tried, we are really just at the start of battery development. There’s a few dozen metals, and a few dozen electrolytes, and carbon and nano-structures, and membranes, and ion barriers and… it could take centuries just to try all of the combinations. (not to mention alloys and surface treatments and physical layouts and temperature regimens and electrolyte mixes and… )

    I’m trying to think of what salt they have that would react with aluminum, but not too much, and with simple electrical reversal… Sodium is used in refining… (he does a web search…)

    http://kohl.chbe.gatech.edu/sites/default/files/linked_files/publications/1995_Stability%20of%20Sodium%20Electrodeposited%20from%20a%20Room%20Temperature%20Chloroaluminate%20Molten%20Salt.pdf

    Stability of Sodium Electrodeposited from a Room Temperature
    Chloroaluminate Molten Salt

    Gary E. Gray,* Paul A. Kahl,** and Jack Winnick**

    Georgia Institute of Technology, School of Chemical Engineering, Atlanta, Georgia 30332-0100, USA

    ABSTRACT

    Room temperature molten salts consisting of 1-methyl-3-ethylimidazo]ium chloride (MEIC) and aluminum chloride A]C13) have been examined as possible electrolytes for a room temperature design of the sodium/iron(II) chloride battery.

    This work examines the conditions required to achieve efficient reduction and oxidation of sodium from a sodium chloride buffered, neutral melt. Two substrates were examined, tungsten and 303 stainless steel, using both cyclic voltammetry and chronopotentiometry. Melts were protonated using a closed electrochemical cell to allow quantification of the effect of dissolved HC1 on the efficiency of the sodium couple. A threshold of approximately 6 Torr HC1 partial pressure was observed for sodium plating-stripping. Below this threshold, the sodium couple was not observed.

    The results show that the sodium plating-stripping efficiency increases with increasing current density; however, the efficiency reaches a maximum and is adversely affected by high overpotentials and extended exposure of the sodium to the melt. It appears that some passivation occurs as even a very thin layer of plated sodium exhibits a steady open-circuit voltage over long periods in the melt.

    Don’t know what MEIC is, but it looks like a likely salt mix. Now add an aluminum electrode and have that AlCl3 be what converts, and a carbon electrode instead of sodium/iron…. Might work.

  3. punmaster52 says:

    Diesel engines (another of my favorite things…)

    High speed diesels in small lightweight sport cars
    these are just two of my favorite things.

    Everybody sing, you know the tune.

  4. E.M.Smith says:

    To make the meter right ought not that be:

    “Big high speed Diesels in small lightweight sports cars”….
    ;-)

  5. punmaster52 says:

    Come in on the second note. :-)
    A big diesel in a small car will throw the balance off.

  6. cdquarles says:

    Fascinating, EM. Is there a link to the x-ray crystallography so I can look at its symmetry forms?

    Stepped edges for catalysis. Guess how enzymes work :). The nice thing about enzymes is that those edges are flexible.

  7. E.M.Smith says:

    @cdquarles:

    I think you are on your own for that. Quick searches on “mullite xray” and “mullite crystallography xray” turns up several papers, but everything was paywalled. So “going to page 2” is up to you.

    The wiki has an interesting tease about “distorted” crystal forms:

    Mullite or porcelainite is a rare silicate mineral of post-clay genesis. It can form two stoichiometric forms 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge balancing cations present. As a result, there are three different Al sites: two distorted tetrahedral sites and one octahedral.
    Mullite was first described in 1924 for an occurrence on

    I suspect that the “doping” with other metal ions also shifts things around.

    http://www.mindat.org/min-2806.html

    has some nice pictures. Also some crystallography data, for example :

    Crystallography of Mullite
    Crystal System:Orthorhombic
    Class (H-M):mmm (2/m 2/m 2/m) – Dipyramidal
    Space Group:Pbam
    Cell Parameters:a = 7.5785(6) Å, b = 7.6817(7) Å, c = 2.8864(3) Å
    Ratio:a:b:c = 0.987 : 1 : 0.376
    Unit Cell Volume:V 168.03 ų (Calculated from Unit Cell)
    Z:1
    Morphology:Crystals prismatic to acicular
    Comment:On synthetic material.
    X-Ray Powder Diffraction Data:
    d-spacing Intensity
    5.39 (50)
    3.390 (100)
    3.428 (95)
    2.694 (40)
    2.542 (50)
    2.206 (60)
    1.5242 (35)

    That’s about the best I can do on a small dive…

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