Synergies of the Zr/Sm Co-doped Fe2O3/CeO2 Oxygen Carrier for Chemical Looping H2 generation.

[NNadir]

The paper I'll discuss in this post is this one: Synergistic Effects of the Zr and Sm Co-doped Fe2O3/CeO2 Oxygen Carrier for Chemical Looping Hydrogen Generation (Xiang et al, Energy and Fuels, 2020, 34, 8, 10256–10267.)

Much of what we hear about energy is delusional. Many people, for instance, believe that so called "renewable energy" is having an effect, or will have an effect "by 'such and such' year" on climate change. This has clearly proved to be nonsense, despite nearly half a century of wild cheering and the expenditure of trillions of dollars for no meaningful result other than an increase in the strength of hurricanes. (The fool Mark Z. Jacobson, of Stanford University has published a deliciously amusing paper claiming that wind turbines can stop hurricanes, which begs the question of whether wind turbines can stop, um, the wind: Taming hurricanes with arrays of offshore wind turbines. (Jacobson et al., Nature Climate Change, volume 4, pages 195–200 (2014))

You hear these sort of things, and you don't believe you're hearing correctly, but one needs to be careful in criticizing Dr. Jacobson, since he's rather Trumpian in the sense that he responds to criticism with lawsuits.

Nevertheless he, is, however, which I say at the risk of a lawsuit, delusional. Wind turbines at sea will do little more than further distribute polymers in seawater when these short-lived pieces of shit transform into greasy landfill or even worse, debris on the seafloor.

Another delusional claim that shows up quite a bit is that hydrogen is a clean fuel. This is nonsense. Barring the development of fusion reactors, hydrogen, as the paper I will discuss correctly notes, is an energy carrier, not a form of primary energy, that is, all of the hydrogen on earth is a form of chemically stored energy. As such, making hydrogen wastes energy, and the question of whether it is sustainable to so waste energy depends on the cleanliness of the form of energy itself. A great deal has been written about hydrogen from wind energy in this century and, in fact, before this century. Since wind power is not a clean and sustainable form of energy, hydrogen from wind is not clean and sustainable. Of course, neither is the main source of almost all the hydrogen manufactured on earth clean and sustainable. Currently 95+% of all hydrogen produced industrially comes from dangerous natural gas. Small amounts are generated as a side product of the chlorine industry, but in general, such production has remained trivial for nearly a century.

In my oft stated opinion - and I fully understand that nobody cares what I think - nuclear energy is the only sustainable form of energy there is. In order to advance the technical feasibility of using nuclear energy to address climate change in such a way as to actually remove the dangerous fossil fuel waste accumulated, hydrogen will be required, as a captive intermediate for fixing and sequestering carbon dioxide in the form of useful products, the only economical and sustainable way carbon can be sequestered, via "CCU," carbon capture and utilization.

Nobody cares what I think, or as Rutger Hauer put it:

I've seen things you people wouldn't believe... All those moments will be lost in time, like tears in rain.

Tears in the rain...there is a world worth saving and I cannot stop myself from saying so, though saving it looks more and more difficult because of the human capacity for self delusion.

"Chemical looping" is a process whereby oxygen is delivered to a combustible material when chemically bound to another substance, and - often in direct contact with the combustible material - causes the material to combust with the release of energy. It is not too much of a stretch to consider hemoglobin in blood operating as a chemical looping process, and interestingly blood, like many proposed approaches to chemical looping, utilizes iron as the carrier, since heamglobin is an iron porphyrin complex at its core.

Industrially, chemical looping is designed to oxidize carbon based fuels in such a way that the exhaust is effectively pure carbon dioxide. If the carbon based fuel is biomass derived, this represents a strategy for direct capture of carbon dioxide from the air.

What caught my eye here is the use of cerium, an element that has been proposed for use in the thermochemical splitting of carbon dioxide into its monoxide and oxygen. (Carbon monoxide is a hydrogen equivalent, via the "water gas" reaction.)

From the paper's introduction:

Hydrogen is not only an ideal energy carrier but also an important industrial raw material widely used in chemical engineering, metallurgy, aerospace industry, etc. At present, hydrogen mostly originated from the reforming of fossil fuels, which would be a complex process and bring about abundant emission of CO2 into the atmosphere.
Chemical looping hydrogen generation (CLHG) is a promising technology, which can generate hydrogen of high purity with inherent CO2 capture.(1,2) It was composed of three consecutively connected reactors, i.e., fuel reactor (FR), steam reactor (SR), and air reactor (AR), and Fe2O3 is the most promising oxygen carrier for CLHG.(3,4) The fuel is oxidized into H2O and CO2 in the FR with Fe2O3 reduction into FeO or Fe; then FeO/Fe is oxidized into Fe3O4 in the SR with hydrogen generated; and Fe3O4 is transferred into the AR with Fe2O3 regenerated.

A support is necessary to improve the redox stability of the Fe-based oxygen carrier, and CeO2, as a typical fluorite oxide, is an active support, which can boost the reactivity and eliminate the carbon deposition of the oxygen carrier through promoting the lattice oxygen conductivity.(5,6) The lattice oxygen conductivity is critical for the redox reactivity and sintering resistance of the Fe-based oxygen carrier.(7?10) Specifically, doping CeO2 with cations with a smaller radius or lower valence can further increase the oxygen mobility because the cations with a smaller radius could decrease the oxygen vacancy formation energy(11,12) and the cations with a lower valence could give rise to more oxygen vacancies for charge neutrality.(13,14)
Zr4+, with a smaller radius (0.084 nm) than Ce4+ (0.097 nm), is the best known and most usually investigated doping cation for CeO2.(13) The insertion of Zr4+ could cause the contraction distortion of the CeO2 crystal cell, reducing the strain to accommodate the larger Ce3+ (0.107 nm), such that oxygen vacancies can be easily generated around the Zr4+ cations, leading to high oxygen mobility.(12,15) Moreover, ZrO2 is a desirable inert support for the chemical looping process with high thermal and chemical stabilities. The CeO2-based solid solution originating from ZrO2 modification always shows high thermal stability and promotes oxygen storage capacity in heterogeneous catalysis, such as three-way catalyst (TWC), catalytic oxidation of CH4, and volatile organic compounds (VOCs).(16?19)

Since the oxidizing reaction involves the use of steam to generate hydrogen, this system is effectively a thermochemical water spitting procedure.

There has been much discussion in the literature on the subject of oxygen permeable transport materials, one class of such materials being perovskites. Perovskites also discussed widely in connection with the useless solar industry, and usually the perovskites in question are lead based; you can have a delicious conversation with stupid people about whether distributing lead for distributed energy is a good idea; I had a wonderful conversation along these lines with a dumb person over in the benighted E&E forum, where one can learn that so called "renewable energy" is saving the world and at the same time learn that climate change is getting worse and worse.

You hear these sort of things, and you don't believe you're hearing correctly...

Several years back I spent a lot of time studying papers on the subject of oxygen transporting perovskites, compiling a spreadsheet of all papers published over a period of time with columns for each element utilized in them to allow for sorting them. From my notes, it seems I abandoned this task around 2015, when I realized that most of these transport perovskites were unstable in the presence of carbon dioxide. Perhaps this paper, as a chemical looping procedure, avoids this problem. I just opened one of those old spreadsheets, and I note the presence therein of a number of papers over the period I was searching involving the elements in this system, notably iron, cerium and samarium.

The authors of this paper offer a note about the use of samarium:

For doping cations in CeO2 with lower valence, rare earth cations with 3+ valence are the most widely used cations.(13) In addition to the promoted oxygen conductivity, it has been found that the rare earth doping could also improve the stability of CeO2. La-doped CeO2 could maintain high lattice oxygen conductivity even after calcination at 1000 °C(28) and shows higher oxygen storage capacity and catalytic oxidation ability than CeO2–ZrO2 mixed oxides.(29) He et al.(30) claimed that CeO2 with Y doping could induce abundant lattice defects and active sites for catalytic decomposition of CH3SH. The oxygen mobility of CeO2-based solid solution is closely related to the species of rare earth elements.(13,31) Sm- and Gd-doped CeO2 have been recognized as the highest oxygen-conductive solid solutions among the rare-earth-doped CeO2.(32?34) Furthermore, the oxygen mobility in CeO2 with Sm dopant is higher than that with Gd as a result of its more oxygen vacancy defects,(35?39) although some controversial findings suggested that Gd-doped CeO2 was superior to that of Sm.(40) Specifically, Anjaneya et al.(41) observed the highest ionic conductivity as well as the lowest activation energy in Ce0.8Sm0.2O1.9, and Yahiro et al.(32) found that the oxygen conductivity of Ce0.8Sm0.2O1.9 was about twice that of Ce0.8Gd0.2O1.9. Given the excellent properties of rare-earth-doped CeO2, they have been applied in the catalytic oxidation of soot, CH4, CO, and VOCs.(14,42?45)

It is worthy to mention that the CeO2–rare earth mixed oxides have also been applied in chemical looping processes. Hedayati et al.(46) indicated that Ce0.9Gd0.1O1.9 could enhance the reactivity and showed satisfactory fluidization, sintering, and agglomeration resistance as a support for CuO, Fe2O3, and Mn2O3 in chemical looping combustion (CLC). Besides, Kosaka et al.(47) reported that Gd-doped CeO2 could promote the reduction of Fe2O3, especially for the deep reduction from FeO to Fe, because Gd-doped CeO2 could enhance the outward mobility of lattice oxygen in the particles. Zeng et al...

...Our group compared rare earth elements, Y, La, and Sm, doped CeO2 as the supports for the Fe-based oxygen carrier in CLHG,(50) finding that Fe2O3/Ce0.8Sm0.2O1.9 was the most active oxygen carrier and had the highest oxygen vacancy concentration; however, the Fe-based oxygen carrier with rare-earth-doped CeO2 as a support exhibited low sintering resistance, exerting a detrimental effect on the reactivity. Considering the excellent thermal stability of ZrO2,(51,52) Zr-doped CeO2 could not only improve the store/release oxygen properties but also promote the thermal stability of the oxygen carrier.(27) Therefore, it could be anticipated that the co-doping of rare earth and Zr into CeO2 as a support for Fe2O3 could bring about desirable performance for CLHG.

The fuel utilized in the "fuel" reactor, is in fact, carbon monoxide in this paper. Because of ash considerations - a consideration in any chemical looping procedure - it is necessary to use relatively pure, or at least ash free fuels in these systems. This is an important caveat, although one can imagine systems for addressing this concern.

Some pictures from the text:



The caption:

Figure 1. (a) XRD patterns of fresh oxygen carriers. (b) Enlarged view for the (111) reflection of CeO2. (c) Enlarged view for the (110) reflection of Fe2O3.

The caption:

Figure 2. H2-TPR patterns of prepared oxygen carriers.

"TPR" here is a technique known as "temperature programmed (hydrogen) reduction" which was utilized to characterize the oxygen carrier. The instrument model is BELCAT-B (MicrotracBEL Japan, Inc.), which is a surface area measuring instrument similar to those for "BET" (Brunauer–Emmett–Teller) surface area measurements.

The hydrogen production reactivity seems to be fairly stable through a number of cycles:



The caption:

Figure 3. Effect of the redox cycle on the H2 yield for various oxygen carriers.

In this paper, nitrogen was utilized as a carrier gas, and thus the system did not produce pure carbon dioxide. This is an issue that would need to be addressed in any attempt to pilot and especially commercialize this sort of system.



The caption:

Figure 4. CO2 concentration in the reduction stage of the 10th cycle.

The caption:

Figure 5. Conversion rates of oxygen carriers in the reduction stage of the 10th cycle.

"Roc" refers to the conversion rate.



The caption:

Figure 6. XRD patterns of oxygen carriers before and after cycles.

The morphology of these material has clearly changed after cycling, but does not seem to have had a huge effect on function. Whether this would be the case for thousands of cycles, as well might be required for any industrial system using this technology, is an open question.



The caption:

Figure 7. SEM images of oxygen carriers before and after redox cycles.

The caption:

Figure 8. EDX analysis of oxygen carriers before and after cycles.

"EDX" is a technique known as "energy dispersive x-ray analysis"



The caption:

Figure 9. XPS O 1s spectra of the oxygen carriers after cycles.

"XPS" is x-ray photoelectron spectroscopy, which measures the energy levels of electrons in the material, giving information about its structure. In this context, it is utilized to measure oxygen vacancies which are necessary for oxygen to migrate in the material.

An excerpt of the conclusion:

...Fe2O3/Ce0.6Sm0.15Zr0.25O1.925 was the best considering the reactivity, redox stability, H2 yield and purity. The reactivity of samples followed the sequence Fe2O3/Ce0.6Sm0.15Zr0.25O1.925 > Fe2O3/Ce0.8Sm0.2O1.9 > Fe2O3/Ce0.75Zr0.25O2 > Fe2O3/CeO2. The Sm dopant was mainly inserted into CeO2, and a small amount of it was doped into Fe2O3. Nevertheless, the Zr dopant could only be doped into CeO2. The Zr and Sm doping could restrain the growth of the CeO2 and Fe2O3 crystallites and alleviate the sintering of the oxygen carrier. Moreover, the Zr and Sm doping could enhance the oxygen mobility of the oxygen carrier and improve the consistency of the reduction extent in the whole particle, and the concentration of oxygen vacancy was ranked as Fe2O3/Ce0.8Sm0.2O1.9 > Fe2O3/Ce0.6Sm0.15Zr0.25O1.925 > Fe2O3/Ce0.75Zr0.25O2 > Fe2O3/CeO2. Both Zr and Sm doping could restrain the outward diffusion of Fe cations to the particle surface, improving the sintering resistance and the redox stability of the oxygen carrier, and the co-doped sample Fe2O3/Ce0.6Sm0.15Zr0.25O1.925 achieved the best performance. Serious sintering occurred for cycled Fe2O3/CeO2, and the Zr doping could enhance the sintering resistance significantly and, thus, improve the reactivity. Nevertheless, the Sm doping promoted the reactivity of Fe2O3/CeO2 mainly by increasing the oxygen mobility, and its improvement effect on thermal stability was quite limited. In addition, both Zr and Sm could be incorporated into CeO2 for prepared Fe2O3/Ce0.6Sm0.15Zr0.25O1.925...

Like tears in the wind...

Little papers like this offer me some hope for a future, smarter generation, in the future.

...tears in the wind...

Wind turbines will not stop hurricanes, because they will not stop climate change.

It's funny this morning, because I often think of nuclear power plants along the coast of the Gulf of Mexico, because I dream of things like refilling the Ogallala aquifer, Lake Owens, the California groundwater aquifers as a path to draining the oceans, while simultaneously cleaning the filth laden Gulf of its oil residues, it's micro and macro plastics, the explosive growth of eutrophication plants, this while recovering precious phosphorous.

These are big dreams, giant dreams, beyond anything of which I am capable, "like tears in the rain." But as I approach the end of my life, these possibilities, the existence of which I have convinced myself, as possibilities as opposed to certainties fill me with blind hope for a future of which future generations may have been robbed.

I can only imagine the paroxysms of stupid concern that the existence of a chain of nuclear power plants powering such a clean up in the Galveston, Lake Charles area might have inspired this morning. Certainly they would drown out any whimpers of concern about the dangerous fossil fuel infrastructure in that area, which is both real, and a far higher risk than anything associated with the big bogeyman at, say Fukushima.

Nuclear power plants wouldn't stop the wind but the could arrest climate change, but could is a conditional word, except in the imagination in which people at Greenpeace, for instance, say list all the things that so called "renewable energy" could do, as if "could" was the same as "is" but, in fact, so called "renewable energy hasn't done, isn't doing, and frankly won't do anything to address climate change.

The climate is shuffling off the weight of humanity. Ironically, the science of thermodynamics, high temperatures in already hot times are required.

This lovely little paper, obscure as the contents may be to the general public, demonstrates how this might be.

I trust you are safe and well in these very challenging, and frankly, frightful times.

[flying_wahini]

1. So I infer that the self propelled cycle is not exactly nuclear in scope?

Just a way of cleaning the contaminated byproducts Of nuclear power. So it’s cleaner
Nuclear Power.

I especially liked the mention of reusing aquifers to filter out all the crap and chemicals from the gulf. Wouldn’t that be wonderful?
Anyway, thanks for posting.

[NNadir]

2. This is a thermal process, and has no intrinsic connection to nuclear power.

My reference to nuclear power is that it is the only sustainable and clean way to produce the high temperatures to generate the steam required to drive this process.

In theory, high temperatures could be provided by the combustion of biomass, but in a very real sense, this would represent a perpetual motion system and is thus not thermodynamically allowed.