Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts

[NNadir]

The paper I'll discuss in this post is this one: Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example (Shangchao Xiong, Jianjun Chen,* Nan Huang, Shijian Yang, Yue Peng and Junhua Li, Environ. Sci. Technol. 2019, 53, 17, 10379-10386)

2019 is the second year in which the weekly carbon dioxide measurements at the Mauna Loa carbon dioxide observatory as compared to the same week in an earlier year, in this case 2018, are averaging more than 3.00 ppm. The exact figure as of this writing YTD is 3.07 ppm. 2016 was the first such year, when in comparison to 2015, measurements ran at 3.40 ppm on average.

The climate catastrophe now under way is precisely that which was predicted two or three decades ago. The essence of science is that if a theory's predictions agree with results, the theory gains credence.

One of the theories we've heard a lot about is that so called "renewable energy" would save the day.

It should be clear to anyone not engaged in Trumpian dishonesty that the bet on so called "renewable energy" didn't work, isn't working and won't work. The use of dangerous fossil fuels is accelerating, not decelerating, as are the increases in the concentration in the planetary atmosphere of the dangerous fossil fuel waste carbon dioxide.

People are literally dropping dead in the streets from heat and still we keep prattling on about wind and solar power, how great they are, how wonderful they're doing, and how popular they are.

History will not forgive us, nor should it.

Carbon dioxide is not, however, the only climate forcing gas, as most people know. The second most important one is methane, which is a side product of the real fastest growing source of energy over the last two or three years, the form of energy for which wind and solar are merely marketing lipstick on the pig, methane, the main constituent of dangerous natural gas. (Coal is the fastest growing source of energy on this planet in the 21st century, although there has been a very, very, slight decrease in its use over the last two years.)

The third most important climate forcing gas is nitrous oxide, famously known as "laughing gas," although in context there's nothing funny about it.

The paper cited gives a nice overview of its risks, because it is not only a climate forcing gas, it is an ozone destroying gas as well. From the introduction:

Nitrous oxide (N2O) emitted from the production of adipic acid and nitric acid, as well as the processes using nitric acid as an oxidant, contributes to the ozone hole and greenhouse effect.(1,2) Its global warming potential is ∼310 times and ∼31 times higher than that of CO2 and CH4, respectively, and the lifetime of N2O is ∼114 years.(3) Moreover, N2O can deplete the ozone layer by a reaction pathway similar to that of chlorofluorocarbons. Previous studies reported that N2O would be the dominant ozone-depleting substance in the 21st century.(4) Thus, the reduction in anthropogenic N2O emissions is urgently required. Several techniques were proposed to control anthropogenic N2O emissions, whereas the direct catalytic decomposition of N2O is regarded as the most promising alternative technique.(5,6) Retrofitting the existing flue gas treatment process to incorporate this technique is relatively convenient and can minimize the economic demands.

While this introduction is accurate so far is goes, one should state that the largest source, by far, of nitrous oxide is not the manufacture of adipic acid and nitric acid. It is agriculture. Without the nitrogen fertilizers from which nitrous oxide derives, we would need to choose to have a large portion of the world's population starve to death. Any volunteers?

Nitrous oxide, despite being an ozone depleting gas, as is the case with other ozone depleting gases is quite unreactive in the absence of radiation, even though it is thermodynamically unstable with respect to elemental oxygen and nitrogen. Substances in this class, thermodynamically unstable but kinetically metastable require catalysts to drive their decomposition, catalysts being the topic of the author's paper.

They continue:

A series of noble metals and non-noble metals were used to catalyze the decomposition of N2O.(6) Noble metals (e.g., Rh and Ru) show a satisfactory N2O decomposition performance at low temperature, but their high cost and poor tolerance to various influential factors (e.g., oxygen and water vapor) extremely restrict their widespread applications.(7−9) Iron-based zeolites (especially Fe-ZSM-5) are another type of N2O decomposition catalyst, which attracted great interest because of their tolerance to O2 and H2O.(10,11) The N2O decomposition activity of Fe-ZSM-5 is even promoted by the presence of NO in flue gas.(12) However, the reaction temperature of iron-based zeolites is quite high, and it is difficult to meet the actual flue gas conditions.

Metal oxides, especially transition-metal oxides, are widely researched and employed in the N2O decomposition reaction, which are consequences of their low price, excellent reducibility, and adequate catalytic characteristics.(13,14) Particularly, metal oxides exhibiting the spinel structure are efficient catalysts to decompose N2O.(15) The metal cations in the spinel structure are in the mixed valence state, which frequently consists of divalent and trivalent states. The divalent and trivalent cations in the spinel structure are located in tetrahedral and octahedral coordination centers and are represented as AIIBIII2O4. Because the key step in the N2O decomposition reaction is generally regarded as the charge transfer from the active sites to the antibonding orbital of N2O, spinels can decompose N2O at a relatively low temperature because of their excellent redox property attributed to the divalent and trivalent cations in the spinel structure.(16,17) Given this perspective, metal oxides with the spinel structure were systematically investigated in the decomposition of N2O.(6) Russo et al. investigated several spinel-type catalysts and found that Co-based spinels can provide the most efficient N2O decomposition performance.(18) However, the redox properties of Co-based spinels are not the best among those of spinel catalysts. Consequently, there must exist another crucial property that significantly affects the catalytic performance of N2O decomposition. Many researchers used density functional theory (DFT) methods to calculate the reaction pathway of N2O decomposition and proposed that N2O adsorption is the first step in N2O decomposition.(15,19) The chemical adsorption of N2O generally follows “N–N–O–□”...(20,21)

Cobalt is a "conflict metal." It is mined by children working under slave like conditions, not that this has prevented lots of people from cheering loudly for its use in putative "green" Tesla electric cars which for reasons that escape me entirely, are popular on the left.

Nevertheless, it is worth considering the paper while keeping this in the back of our minds. Enslaved children are not really mollified I'd guess by the existence of "green" electric cars, but in any world where they are justly treated, not the one in which we live, nitrous oxide will matter, for the just, the unjust, the free, the slave, the rich, the poor.

...Herein, the N2O decomposition mechanism and the key roles of CuO and Co3O4 spinel in CuxCoy mixed oxides were systematically investigated by a kinetic study combined with DFT, in situ diffuse reflectance Fourier transforms, N2O-temperature program desorption (TPD), H2-TPR and X-ray photoelectron spectroscopy (XPS) studies. The crucial properties of CuxCoy catalysts and the connection between the physicochemical properties and the kinetic study were proposed.

The paper gives experimental and modeling (DFT) details.

Some graphic results:



The caption:

Figure 1. (a) N2O decomposition performance of the Co3O4, CuxCoy, and CuO catalysts. (b) N2O decomposition performance of Cu2Co1 under different conditions. Reaction conditions: [N2O] = 1000 ppm, [O2] = 2% (when used), [NO] = 200 ppm (when used), [H2O] = 0.5% (when used), catalyst mass = 100 mg, flow rate = 100 mL min^(–1), and GHSV = 60 000 cm3 g^(–1) h^(–1).

The caption:

Figure 2. (a) H2-TPR profiles of the Co3O4, CuxCoy, and CuO catalysts. (b) Initial H2 consumption rates of the CuxCoy and CuO catalysts in the H2-TPR study.

TPR is a technique known as "temperature program reduction" utilized to characterize the efficiency of catalysts by using a reducing gas, here hydrogen.



The caption:

Figure 3. (a) AES spectra of the CuxCoy and CuO catalysts for the spectral region of the Cu LMM. (b) XPS spectra of the Co3O4 and CuxCoy catalysts for the spectral region of the Co 2p3/2.

The caption:

Figure 4. Model structures of N2O adsorbed on: (a) CuO, (b) CuO with an oxygen vacancy, (c) Co3O4, and (d−f) Co3O4 with an oxygen vacancy. The white balls represent N, red balls represent O, blue balls represent Cu, and navy-blue balls represent Co. (g) N2O desorption amounts during N2O-TPD over Co3O4, CuxCoy, and CuO catalysts.

The caption:

Figure 5. N2O decomposition rate constants of the Co3O4, CuxCoy, and CuO catalysts.

Note the high temperatures at which the decomposition is most effective for all of the catalysts herein described. This is another case where environmental remediation - were we to give a rat's ass (we don't) about the future of humanity - would require energy, clean energy, which um, disqualifies the mass intensive solar and wind industries which will never be clean, and which will never be anything more than a foot note to the methane industry.

The mechanism of the decomposition:



The caption:

Scheme 1. Key Roles of CuO and Co3O4 in the CuxCoy Catalysts for N2O Decomposition

From the conclusion to the paper:

Based on the above results and conclusions, the N2O decomposition mechanism over CuxCoy catalysts and the key roles of CuO and Co3O4 in CuxCoy catalysts for N2O decomposition were proposed (Scheme 1). The DFT calculation results suggest that Co3O4 provided abundant surface oxygen vacancies, and thus, served as the major adsorption site of N2O. CuO was dispersed around Co3O4 and provided high reducibility on the interface of Co3O4–CuOx, which promoted the rate-determining step (N–O break) of N2O decomposition and left O in the defect sites. Meanwhile, the charge interaction became stronger with the increasing Cu content and promoted the formation of Cu+ and Co2+, which performed as the active sites and adsorption sites, respectively. Finally, the residual O in the defect sites recombined to release O2.

It is worth noting that one of the uses for nitrous oxide is in a gas phase radiation dosimeter. Radiation destroys this dangerous gas, negating the necessity for a catalyst. In fact, radiation in the upper atmosphere does precisely this, albeit at the environmental expense of destroying the planet's protective ozone layer.

This suggests a use for components of used nuclear fuels, the irradiation of air at tropospheric levels to destroy this dangerous gas, were we to ignore the idiot prattling of anti-nukes and choose to do something meaningful to address the wholesale destruction of the atmosphere.

A few years ago, on this website I took to noting, after decades of hearing horseshit about how so called "renewable energy" was somehow superior to nuclear energy - which it isn't even close to being since mining iron and coal to make steel posts for wind turbines that become garbage in less than 20 years is in no way "green" - that no one now living will ever see the concentrations of dangerous fossil fuel waste in the atmosphere of less than 400 ppm. It is now September, and we are approaching the annual minimum for carbon dioxide concentrations, which now stand well above 408 ppm. Thus just a few years after I began using the statement about how "no one now living will ever see the concentrations of dangerous fossil fuel waste in the atmosphere of less than 400 ppm," we can now substitute "408" for 400.

Next year will be worse.

Wonderful, isn't it?

We should pause to wonder what an "environmentalist" actually is. Despite the pixilated nonsense put out by the insane media, "Greenpeace," has nothing to do with environmentalism.

I have noticed recently that a few of my posts in this section have produced more comments than I can actually read. I if not humanity have chosen to ignore the insane prattlings of anti-nukes. They simply infuriate me, since their ignorance kills people and we should choose not to dignify such deadly nonsense with comment.

I trust you've enjoyed the weekend.

[eppur_se_muova]

1. Interesting post, but did you mean to post in E/E ??

Lots of scientific data, sure, but implications would be of interest to E/E readers, no ?

[NNadir]

2. No. If it's all the same to you, I prefer to post reference...

...to environmental science in the science forum.

I question whether the E&E forum is involved with science per se and as a scientist, I am less and less inclined to post there at all since the majority of my posts refer directly to scientific literature.

The issue herein in this post is about our shared profession, chemistry, in this case atmospheric chemistry. My opinion is that it is entirely appropriate here.

Let me know if you disagree either publicly or privately.

[eppur_se_muova]

3. Not saying it's inappropriate, just might get some more eyeballs in E/E ...

... including some who might not notice it in our sleepy little Science group.

PS: While it's well outside my own area of expertise, the problem of NOx is something that's often in the back of my mind ... so I did find it interesting, whatever group it's posted in.

[NNadir]

4. The general public finds science "sleepy" at its own peril.

This is true across the political spectrum.

We like to make fun of the right, but here on the left we can be just as bad.

The results of the rhetoric advanced over in E&E are in; no one alive will ever see a measurement of carbon dioxide at Mauna Loa below 405 ppm again.

Nevertheless, the rhetoric continues unchanged.

That's not consistent with science. We famously believe that repeating the same thing over and over again expecting a different result is insanity.