More Lipstick on the Gas Pig: Dry Reforming Methane with "Solar" Thermal Energy.

[NNadir]

The paper I'll discuss in this post is this one: Photothermocatalytic Dry Reforming of Methane for Efficient CO2 Reduction and Solar Energy Storage Shaowen Wu, Yuanzhi Li, Qianqian Hu, Jichun Wu, and Qian Zhang ACS Sustainable Chemistry & Engineering 2021 9 (35), 11635-11651.

You here from time to time from people with rather glib wishful thinking that hydrogen is so called "green" energy because its combustion product is "only" water.

Despite oodles and oodles and oodles and oodles of papers in the literature, and hundreds of thousands of internet posts about "green" hydrogen made with so called "renewable energy," where so called "renewable energy" is defined largely by solar and wind energy, the overwhelming amount of hydrogen produced on this planet is produced from the reformation of dangerous natural gas at high temperatures, the temperatures being provided by burning dangerous natural gas and dumping the dangerous natural gas waste carbon dioxide into the atmosphere without restriction.

That's a fact.

Facts matter.

So called "renewable energy cannot survive without access to dangerous fossil fuels and this paper, which bills itself as an energy storage paper - energy storage is by definition an exercise in wasting energy (unless it recovers energy that would have been wasted anyway) - is no exception.

"DRM" in the context of this paper, is referred to as "dry reforming of methane." Dry reforming is a well known technology in which carbon dioxide is utilized as an oxidant, and in turn is converted to carbon monoxide. Dry reforming is possible with many carbon compounds; the dangerous fossil fuel methane, the chief component of dangerous natural gas just happens to seem cheap, because the real costs will be paid by future generations, about whom the current generation couldn't give a rat's ass.

This paper is, about solar reforming. In these times any appalling and unsustainable practice can be greenwashed simply by sticking the word "solar" on it and assuming most people are too lazy to see through it, generally a good bet for advertisers.


From the text:

Due to the combustion of fossil fuels, CO2 as a greenhouse gas is discharged in enormous quantities in various industrial processes. It causes two major global strategic issues such as global warming and energy shortage. Developing strategies to address the two issues is very important for a sustainable society. Solar light is inexhaustible energy. Its efficient utilization provides a very promising solution to the energy shortage. Photovoltaics can efficiently convert solar energy to electricity, thus acquiring wide application.(1) As solar light is only available in the daytime, solar energy storage is highly desirable. Extensive works have been devoted to develop strategies for efficient light-to-fuel conversion for decades. The strategies involve photocatalytic H2O splitting,(2−12) light-driven thermochemical splitting of H2O or CO2,(13−20) photocatalytic CO2 reduction to produce fuels,(21−41) photocatalytic steam reforming of methane (SRM),(42−50) photocatalytic dry reforming of methane (DRM),(51−60) and so on. Among the strategies, light-driven thermochemical CO2 splitting, photocatalytic CO2 reduction, and photocatalytic DRM are very promising, as the two major global issues could be solved at the same time.


Light-driven thermochemical CO2 splitting involves two steps such as the decomposition of appropriate metal oxides at very high temperature (usually above 1600 °C) and the oxidation of the reduced metal oxides by CO2 to produce CO by using very high concentrated solar illumination (e.g., 1500 suns).(13,14) The major challenge is the difficulty of realizing the decomposition of metal oxides with moderate concentrated solar illumination due to the thermodynamic limit of metal oxide decomposition. Photocatalytic CO2 reduction and DRM involves CO2 reduction by electrons and the oxidation of H2O or organic compounds (e.g., CH4 for DRM) by holes on semiconductor photocatalysts. Extensive works have been devoted to improve the fuel production rate (rfuel) and light-to-fuel efficiency (η values by increasing the separation efficiency of charge carriers and/or reducing the band gap of semiconductor photocatalysts.(21−41,51−58) Low rfuel and η values are the major issues still to be tackled owing to the challenges as follows. First, the majority of charge carriers rapidly recombine, resulting in the absorbed solar energy being lost via thermal energy.(61,62) Second, the η of photocatalysis not only relies on the charge carriers’ separation efficiency like photovoltaics, but also their transfer and reaction efficiencies, inevitably resulting in a low η value.(21) Third, owing to the band gap matching requirement, it is very difficult to design low band gap photocatalysts that are able to use the about 50% of infrared energy in solar light.(21) Therefore, developing a strategy of substantially boosting the rfuel and η values is of great challenge.

I've been hearing all kinds of wonderful stuff about solar thermal technologies my whole adult life by the way, and I'm not by any stretch young. Nevertheless, despite all this cheering, we saw concentrations of 420 ppm of the dangerous fossil fuel waste carbon dioxide in the planetary atmosphere this spring, less than ten years after we first saw 400 ppm.

Facts matter.

The authors continue:

In this Perspective, the recent progress in realizing highly efficient CO2 reaction and light-to-fuel conversion by photothermocatalytic DRM will be summarized. In the Light-Driven Thermocatalytic DRM section, the approach of realizing highly efficient CO2 reduction through photothermocatalytic DRM will be summarized, and the mechanism of light-driven thermocatalytic DRM will be discussed. In the Light-to-Fuel Conversion section, the approaches of realizing efficient light-to-fuel conversion by utilizing the strong endothermic characteristics of DRM and enhancing light-to-fuel efficiency will be discussed. As the major challenge for the photothermocatalytic DRM is the rapid catalyst deactivation owing to the thermodynamically inevitable side reactions of coke formation accompanying DRM, the strategies of kinetically inhibiting coke formation by designing nanostructured group VIII metal catalysts will be summarized, and the mechanism of inhibiting coke formation will be discussed in the Inhibition of Catalyst Deactivation section. As light not only plays a heating role as discussed above, but also plays an interesting photoactivation role of considerably enhancing catalytic activity and inhibiting coke formation in photothermocatalytic DRM, the important photoactivation role will be discussed in the Photoactivation section.

Although most of what is written in this paper is disturbing, to me at least, there is some useful science in it, a nice mini-review of sorts of dry reforming.

To wit:

DRM is a strong endothermic reaction. Thermodynamic analysis shows that DRM starts to occur above 250 °C at atmospheric pressure.(99) When the temperature increases to 540 °C, CO2 and CH4 conversions reach up to 50%. When the temperature increases 700 °C, CO2 and CH4 conversions reach up to about 88% and 92%, respectively.(104) Therefore, to realize photothermocatalytic DRM, the surface temperature of the catalyst under illumination should be above 250 °C at least. To achieve a satisfactory conversion, the temperature usually needs to be above 600 °C. This means that a concentrated illumination source is necessary. To realize photothermocatalytic DRM, effectively avoid thermal energy loss, and maintain the reaction temperature under concentrated illumination, a proper photothermocatalytic reactor is required. More importantly, rationally designing a good catalyst is especially pivotal to efficient photothermocatalytic DRM as the catalyst can not only facilitate the reaction rate but also improve the light utilization efficiency.

With these ideas in mind, a gas-phase reactor for photothermocatalytic DRM (Figure 1A) was designed.(87) Focused illumination from a 500 W Xe lamp was used to drive the reaction. No additional heater is used besides the Xe lamp. A nanocomposite of Pt nanocrystals (with average particle size of 2.1 nm) partially confined in mesoporous CeO2 nanorods (Pt/CeO2-MNR) was prepared. A known amount of the catalyst was put in a thermal insulation sample holder to reduce heat loss. A feed stream of CH4 and CO2 was continuously fed into the reactor.

Note the Xe lamp. One would think that more than half a century into wishful thinking about how solar energy would save us - many of us having bet the future of humanity on this unproved supposition - that there would be lots and lots and lots of handy solar thermal reactors lying around with which to do experiments. This however, would involve scientists working on grants, some working for Ph.Ds. to be able to work only when the sun is shining brightly and hotly. This would limit the lab time, so xenon lamps are used as a surrogate.

This should tell you something.

Don't worry. Be happy. Let's just look at the pictures from the text and feel all fuzzy inside.

The introductory cartoon:



A picture of the apparatus with the xenon lamp:





The caption:

Figure 1. Schematic illustration of a reactor for photothermocatalytic DRM under focused illumination (A). Reaction rates (B) and production rates (C) of Pt/CeO2-MNR (1.0 wt % Pt), Pt-L/CeO2-MNR (0.5 wt % Pt), CeO2-MNR, and TiO2 (P25) for DRM under focused UV–vis–IR illumination. Reaction rates (D) and production rates (E) of Pt/CeO2-MNR under focused vis–IR illumination.(87)

Reference 87 is this one: Solar-light-driven CO2 reduction by methane on Pt nanocrystals partially embedded in mesoporous CeO2 nanorods with high light-to-fuel efficiency† (Li et al, : Green Chem., 2018, 20, 2857)

The work was performed in China, and the odds are overwhelming that the Xenon lamp was produced using electricity generated in a coal fired plant.

Nevertheless if you want to do so, and many people do like to read this kind of garbage, you can head over to read rhetoric by a blatantly dishonest bunch of disingenuous horseshit by an anti-nuke telling us how, in China, so called "renewable energy" had defeated the nuclear industry, using all kinds of misleading charts and graphs designed around the assumption you're stupid:

An Exercise in Bad Thinking: Nuclear In China Shows Clear Scalability Winners The barely literate dweeb who wrote this piece and published it in the year we first saw 420 ppm of the dangerous fossil fuel waste carbon dioxide in the atmosphere, less than 10 years after we first saw 400 ppm of the same waste now setting the planet afire, like most anti-nukes, is interested in so called "renewable energy" as an attack on the only climate change tool that actually works, nuclear energy, and couldn't give a rat's ass about dangerous fossil fuels, the use of which is growing, not falling. His name is Michael Bernard, and he wants you to know that he knows Leonardo Di Caprio and that he's willing to consult for you, presumably for a fee.

If you don't know what you're talking about, make stuff up.

His triumphal account includes a picture which I personally find disgusting, of a huge stretch of land covered by soon to be electronic waste, which may be, for a short period of a day, be able to produce as much power as a nuclear plant on less than 15 acres can produce reliably, night and day, 24/7, 365.25 days per year.

Land use changes are second only to the indiscriminate dumping of dangerous fossil fuel waste in driving carbon dioxide concentrations ad climate change.

Feel Free to call on him if you think the laws of thermodynamics should be repealed.



The caption:

Figure 2. Optical absorption spectra of Pt/CeO2-MNR and CeO2-MNR (A). Time course of production rates for photocatalytic DRM on Pt/CeO2-MNR under UV–vis–IR illumination at near room temperature (B). Schematically illustrated light-driven thermocatalytic DRM on Pt/CeO2-MNR (C). The Teq values of the samples and the sample holder under focused UV–vis–IR illumination (D). Thermocatalytic activity of Pt/CeO2-MNR for DRM in the dark at different temperatures (E and F).(87)

The caption:

Figure 3. Schematically illustrated Cu–single-atom Ru alloy catalyst (A). Reaction rate (B) and selectivity (C) of the catalysts under focused UV–vis–IR illumination. Light-to-fuel efficiency of Cu19.8Ru0.2 as a function of illumination intensity (D).(91)

Ruthenium is a relatively rare element, but it can be obtained from used nuclear fuels as it is a fission product.



The caption:

Figure 4. Optical absorption (A), production rates (B), and the η values (C) of the catalysts under focused UV–vis–IR illumination. The η values of Co/Co–Al2O3 under focused vis–IR illumination (D).(93) (Reprinted with permission from ref (93)

The caption:

Figure 5. XRD patterns (A), HAADF-STEM image (B), line-scan EDX profiles (C and D), and the HAADF-STEM image (E) of SCM-Ni/SiO2. The structurally optimized SiO2/Ni36 slab (F).(115)

The caption:

Figure 6. Thermocatalytic activity in the dark vs reaction time for DRM on SCM-Ni/SiO2 (A) and R-Ni/SiO2 (B) at 700 °C. The relative free energies of the elementary steps for DRM on the slabs of SiO2/Ni36 (C and D) and Ni36 (E and F).(115)

The caption:

Figure 7. HAADF image (A), element mappings (B–D), and high-resolution HAADF-STEM image (E and F) of Co/Co–Al2O3.(93)

The caption:

Figure 8. Schematically illustrated coke formation mechanism for Ni/Al2O3 (A) and coke inhibition mechanism caused by a CO2 molecular fence around a Ni nanoparticle for Ni/Mg–Al2O3 (B).(123) (Reprinted with permission from ref (123).

The caption:

Figure 9. rCH4 and rCO2 values vs T (A) and Ln(rCH4) vs 1/T (B) for DRM on Ni–CeO2/SiO2 (a) in the dark and (b) under focused UV–vis–IR illumination. Energies of the elementary steps through the C oxidation pathway and CH oxidation pathway for DRM on a CeO2/Ni36 slab in the excited states (C and D) and ground states (E and F).(119)

The caption:

Figure 10. CO-TPD profiles (A) and coke formation rates (B) of Co/Co–Al2O3 under UV–vis–IR illumination and in the dark.(93)

The caption:

Figure 11. CO (A) and H2 (B) profiles for CO2-TPO-C of Ni/Mg–Al2O3 under UV–vis–IR illumination and in the dark.(123)

The caption:

Figure 12. Catalytic activity under focused UV–vis–IR illumination (19.2 W cm–2) and in the dark for DRM on Cu19.8Ru0.2 at the same reaction temperature (A). Ground (dark curve) and excited-state (color curves) energy curves for C–H activation on CuRu (111) (B).(91)

The caption:

Figure 13. Production rates (A) and H2/CO ratio (B) for DRM on Ni/Ga2O3 under photothermocatalytic and thermocatalytic conditions. In situ DRIFTS spectra in the range of 2225–1950 cm–1 (C) and 3800–3700 cm–1 (D) for DRM on Ni/Ga2O3 under UV–vis illumination and in the dark.(126) (Reprinted with permission from ref (126).

Gallium is a critical element. The world will run out of methane, the sooner the better from my perspective, but the costs of using this methane in our generation will remain with humanity as long as humanity exists.

Have a nice evening.