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NNadir

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Current location: New Jersey
Member since: 2002
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Electrolytic reduction of carbon dioxide to formate using low over-voltages.

Here's a fun paper: Highly Selective Reduction of CO2 to Formate at Low Overpotentials Achieved by a Mesoporous Tin Oxide Electrocatalyst (Rahman Daiyan, Xunyu Lu*, Wibawa Hendra Saputera, Yun Hau Ng , and Rose Amal* ACS Sustainable Chem. Eng., 2018, 6 (2), pp 1670–1679)

Let me tell you something: Anyone with a name like Wibawa Hendra Saputera is definitely cooler than I will ever be, probably cooler than you'll ever be too.

Here's the introduction to the paper, what it's about:

Rising level of CO2 accumulation in the atmosphere has attracted considerable research interest in technologies capable of CO2 capture, storage, and conversion.(1-3) The electrochemical reduction of CO2 into high-value liquid organic products could be of vital importance to mitigate this issue.(4, 5) The direct conversion of CO2 to liquid fuel using renewable energy, which can readily be integrated with the current infrastructure, will help realize the creation of a sustainable cycle of carbon-based fuel that will promote zero net CO2 emissions.(6-10) Despite initial promising findings, significant progress is required in improving the production rate, efficiency, stability, and cost to make this technology realistic for large-scale utilization.(7, 11)

The current benchmarking electrocatalysts for CO2RR to formate (HCOO–) are sp group metals, notably, Pb, In, and Sn.(12-19) Among the high-performing materials, Sn-based catalysts are especially favored due to their relative low cost, abundance, and nontoxic properties, compared to Pb and In catalysts.(20) Sn catalysts however exhibit certain characteristics, for instance, the local chemical structure of Sn is shown to play a major role in CO2RR, as the bulk Sn foils are reported to have inconsistent formate Faradaic efficiency (FEHCOO–) at a wide range of potentials.(16, 21) To address such discrepancy in catalytic performances, numerous studies on the effect of electrolyte, pH, morphology, and catalyst deactivation for CO2RR with Sn-foil-based catalysts have been undertaken.(22-25) In spite of the insights and understanding into the mechanisms obtained by such studies, Sn-foil-based catalysts still require large overpotentials to attain high values of FEHCOO–. For example, three-dimensional Sn foam grown on Sn foil catalysts require a large applied potential of −1.3 V (vs RHE, applies for all potentials mentioned in this study) to achieve a FEHCOO– of 90%.(26) Similarly, the heat-treated Sn dendrite electrodeposited on Sn foil is also reported to convert CO2 to formate with a moderate FEHCOO– of 71% but this is also done at a large negative applied potential of −1.35 V.(22)


With all due deference to Wibara, this statement is a little off:

The direct conversion of CO2 to liquid fuel using renewable energy, which can readily be integrated with the current infrastructure, will help realize...


The current infrastructure contains very little so called "renewable energy;" overall the fraction of fossil fuels representing world energy portfolios is rising, not falling. In 2000, 80% of world energy came from dangerous fossil fuels. In 2016 (the latest data available) 81% of world energy came from dangerous fossil fuels.

Capturing carbon dioxide using electrical infrastructure that is almost entirely fossil fuel based is simply a perpetual motion machine.

But in theory, if not in practice, clean electricity is potentially available, albeit not from so called "renewable energy.'

No matter.

Some cool pictures of how they make their tin oxide mesoporous catalyst:



The caption:

Scheme 1. Fabrication of m-SnO2 Catalyst


A description of what's going on:

Mesoporous SnO2 was prepared by nanocasting method using KIT-6 as the hard template. KIT-6 was fabricated using an established method.(46) Briefly, 2 g of P123 (Pluronic P-123, Sigma-Aldrich, 99%) was dissolved in 72 mL of deionized water, followed by the addition of 2.5 mL of HCl. Then 2.47 mL of butanol was added dropwise and the mixture was stirred for a duration of 1 h at 35 °C. The solution was then transferred to a hydrothermal reactor and heated to 100 °C for 24 h. The solid product formed was then filtered and calcined at 600 °C for 5 h. To prepare mesoporous SnO2, 1.75 g of tin(IV) tetrachloride pentahydrate (SnCl4·5H2O, Sigma-Aldrich, 99%) was dissolved in 30 mL of ethanol. Then 0.6 g of KIT-6 was added and the mixture heated to 70 °C to evaporate ethanol. The sample was then calcined at 600 °C for 3 h. The impregnation and the calcination process were repeated again with two thirds of the Sn precursor used in the first step to complete the nanocasting process. The KIT-6 templates were then removed by washing the calcined powder twice in a hot 2 M NaOH solution. The resulting samples were collected by repeated centrifugation and washing with deionized water.


KIT-6 is mesoporous silica. I don't know how it's made, but I could look it up, but I'm short on time.

Here's some micrographs of the product anyway:



One of the interesting things about this paper is that the species being reduced is not carbon dioxide but rather the potassium bicarbonate salt. Electrolytic reduction of carbon dioxide is always limited by the low solubility of the gas in water, however the bicarbonate salt (which is made by the absorption of carbon dioxide into basic solutions) is very soluble.

The conclusion:

In summary, mesoporous SnO2 catalyst prepared by a simple and facile nanocasting method using a hard template was successfully employed as a novel electrocatalyst for the selective conversion of CO2 to HCOO–. The as-synthesized catalyst was capable of reducing CO2 to HCOO– with high efficiency and current density at low overpotentials and demonstrated a maximum Faradaic efficiency of 75% and a large current density of 10.8 mA cm–2 at an applied potential of −1.15 V. The results presented herein also demonstrated the high stability of the m-SnO2 electrode toward CO2RR, displaying a stable current density and Faradaic efficiency with no observable decay over 16 h of operation. The improved catalytic activity of the m-SnO2 electrode was ascribed to (i) preferential exposure of crystalline facets that provides sufficient active sites for CO2RR, (ii) significant presence of oxygen vacancy defects, and (iii) enhancement of CO2RR reaction kinetics due to reduced impedance and greater transport of reactants and facile dissipation of products through the large mesopores and well-dispersed catalyst.


Because we have been disinterested in their fate, future generations will need to clean up our carbon dioxide mess, and will need to do so with diminished resources, basically the trash we leave them.

In this regard, this is an interesting paper, since things like this may give them something to work with.

Have a nice evening.



Platinum Group Metal Extraction With Thermomorphic Ionic Liquids.

Many elements in the periodic table are subject to depletion from ores in near term; others in the long term.

Those subject in the short term include the "platinum group metals" - often referred to in the scientific literature as "PGM."

These are the elements, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt).

The first three elements are common fission products that can be isolated from used nuclear fuels. Two of them, ruthenium and rhodium can be obtained in a non-radioactive form with a few decades of cooling; pure non-radioactive (but monoisotopic) Pd can be obtained from the decay of ruthenium-106, which has a half life a few days longer than a year.

Palladium that is isolated as a fission product will remain slightly radioactive for millions of years, owing to the long lived isotope Pd-107. From my perspective this does not mean it is not useful; it can be used as a catalyst (one of the big uses for palladium) in closed systems, and off line I've been considering it as a component of superalloys that would prove superior (higher melting) to the nickel based superalloys which plays a key role in many technologies, notably power generation. The longer the half-life of an isotope, the lower its specific activity; which is why bananas, radioactive because of the potassium they contain, don't kill you. K-40 has a half-life of billions of years.

In the next few years, rhodium will become more available from used nuclear fuels than it is from domestic ores.

It is thus with interest that I came across a paper in the literature today that mentions the extraction of these valuable elements from used nuclear fuels, this one: Significant Acceleration of PGMs Extraction with UCST-Type Thermomorphic Ionic Liquid at Elevated Temperature (Arai et al, ACS Sustainable Chem. Eng., 2018, 6 (2), pp 1555–1559.

The authors describe an "ionic liquid" that is useful for the extraction of the light PGM from used nuclear fuel, where they are considered problematic because they interfere with the bad idea of throwing the stuff in used nuclear fuel away, that is dumping it. (This is a bad idea because all of the components of used nuclear fuel are potentially very useful materials to have. We need more of the stuff, not less, even if as a culture we're generally too stupid to figure that out.)

Here's what they say in their introduction which I've just echoed above:

Ionic liquids (ILs) are commonly defined as organic salts which melt below 100 °C. They have unique properties, e.g., nonflammability, nonvolatility, high conductivity, and diversity of combinations of cations and anions. Specifically, it is possible to synthesize an IL with potential to extract metal ions (Mn+) due to introducing functional groups on either its cationic or anionic components. Because of these properties, the use of ILs as an extraction solvent for Mn+ has been frequently investigated.(1-8) The above characteristics make these extraction systems more environmentally friendly compared with the ordinary organic/aqueous biphasic systems. One of expected applications is treatment of radioactive wastes.(9) For example, platinum group metals (PGMs) like Ru, Rh, and Pd in the high-level liquid wastes are sometimes problematic in the vitrification process.(10, 11) Hence, removal of these PGMs is significantly required. In this context, we are investigating the potential of ILs in the PGMs extraction. A few ILs undergo a temperature-responsive behavior, which shows transition of miscibility of IL with an aqueous solution at a critical temperature.(12-17) Specifically, an IL consisting of N,N,N-trimethylglycinium (or betainium, [Hbet]+) and bis(trifluoromethylsulfonyl)amide ([Tf2N]− ) is hydrophobic enough to form an organic phase immiscible with water at room temperature, whereas these layers are completely miscible with each other above 55 °C, namely, the upper-critical solution temperature (UCST).(18-24) Therefore, [Hbet][Tf2N] (Figure 1(a)) is highly promising for an energy-saving extraction process because ultimately homogeneous mixing of the aqueous/IL biphasic system is facilitated only by heating.


Whenever I look at a new chemical these days, I try to reflect on its environmental fate based on my general knowledge of biochemistry and toxicology. This is why I'm horrified at the latest trend in "green" solar technology, the perovskites, because these are compounds of the toxic element lead, which is even worse than the use of the toxic element cadmium used in commercial solar cells being distributed today with complete disregard for all future generations and too much regard for fads.

Things with a shorter half-life in the environment are obviously better than those with longer half-lives. The best case is compounds that occur naturally.

As it happens, you contain ionic liquids and would die without them. This is choline, which is trimethylammonium ethanol amine chloride (or hydroxide), the cation being an peralkylated and reduced form of the amino acid glycine (albeit not biochemically synthesized from glycine, but rather from serine or methionine.)

Anyway...

Since used nuclear fuels have a very high energy to mass ratio, one should - with a little chemical sophistication - require trivial amounts of materials to process them, but this said, this has historically not been true, as we have learned from the interesting case of the Hanford tanks from the former weapons plutonium isolation plant in Washington State. (The interesting chemistry of these tanks is fascinating, by the way, but that's a topic for another day.)

Here is the structure of the ionic liquids that may prove useful for the extraction of PGM from used nuclear fuels:



The ion on the top left is betaine, a common constituent of plants that helps plant cells balance their osmotic pressure. The ion on the top right is dehydroxycholine; I'm not aware of its presence or lack of presence in living cells, but I image it's going to be metabolized much like either choline or betaine.

The ion on the bottom of both species is however, is bistrifluromethylsulfonyl imide. This is a derivative of triflate, a common reagent utilized as a protecting group in organic synthesis. Triflate is the salt of trifluorosulfonic acid, one of the more powerful acids in the world and regrettably, an acid that is extremely stable. It is therefore environmentally suspect, since it is likely to persist for a long time, rather like the problematic PFOS side product of the Teflon industry and the fabric protection industry, widely distributed, long lived and rather suspect as a potential carcinogen.

I would suspect that triflate might be subject to some radiological degradation, but a lot of radiation in the presence of lots of water would be required, which is why the stuff is good for processing nuclear fuels, but potentially problematic unless completely recovered and recycled.

Anyway, this ionic liquid is very good at the removal of PGMs not only from nuclear fuels, but from other materials from which they may need recovery, at least when they are heated in low concentrations of nitric acid. (PGM are very, very, very, very useful elements.)

A graphic from the paper:



The caption:

Figure 5. Dependence of the extraction efficiency (E%) of Mn+ on [HNO3] in HNO3(aq)–[Hbet][Tf2N] systems.


They may also be useful for partial separations from one another, given their differening distribution constants:



The caption:

Figure 6. Distribution ratio (D) of Ru(III), Rh(III), and Pd(II) as functions of (a) [[Hbet]+] in 0.3 M HNO3(aq)/[TMPA][Tf2N] and (b) [H+] in (H,Na)NO3(aq)/[Hbet][Tf2N] (total [NO3–]: 3.00 M). Initial condition: [Ru(III)] = 7 mM, [Rh(III)] = 3 mM, [Pd(II)] = 5 mM, T = 353 K.


The authors conclude thusly:

To answer what drives the extraction of inert PGMs from HNO3(aq) to the thermomorphic [Hbet][Tf2N] ionic liquid, we studied the distribution behavior of Ru(III) and Rh(III) at different temperatures as well as that of Pd(II), the labile PGM. As a result, the kinetics of the extraction reactions of the inert PGMs were successfully improved at elevated temperatures. Their interaction with [Hbet]+ to form extractable species is the rate-determining step, which has been successfully accelerated by convection heating. Thus, the extraction of these inert PGMs seems to be simply temperature controlled regardless of the heating methods like convection and microwave. The extraction mechanism of Ru(III), Rh(III), and Pd(II) in the current extraction system is concluded to follow the formation of the PGM:bet complexes to release H+ to the aqueous phase. Further detailed investigations are currently ongoing, for instance, separation from other Mn+, preparation and characterization of the extractable PGM:bet complexes, and stripping behavior of the extracted PGMs from [Hbet][Tf2N]. We wonder that the back-extraction kinetics would also be affected by the temperature.


The subtext of this is that despite public fear and ignorance, there are still some people intelligent enough to be figuring out what to do with used nuclear fuels. This can only be good for a future that may prove inhabited by wiser people than we have proved to be.

Have a nice day tomorrow.




Emily Carter Predicts Low Temperature Photodissociation of Nitrogen Gas Bonds.

Although nitrogen comprises about 78% of the planetary atmosphere, living things cannot utilize it in its native state, and until the early 20th century, all of the bioavailable nitrogen depended on nitrogen fixing bacteria, often (on land) in symbiotic association with legumes. The enzymes responsible are probably iron based biocatalysts. (cf. PNAS 2006 November, 103 (46) 17107-17112 (A thermophilic nitrogen fixing bacteria is also known (cf Science 15 Dec 2006:Vol. 314, Issue 5806, pp. 1783-1786 - it or a similar organism may have played a role in the evolution of life on earth.)

In its diatomic elemental form nitrogen is extremely non-reactive. In fact, many chemical reactions in the lab are conducted under pure nitrogen gas (or semi-pure nitrogen in which the other constituent is argon) because the gas is considered inert, a kind of honorary noble gas.

One of the most important industrial chemical reactions on which our food supply depends is the Haber-Bosch process for breaking the triple bond in N2 gas, which liberated humanity from dependence on legumes for nitrogen fixation. (There is no physical way world population today could subsist on biologically fixed nitrogen; without industrially fixed nitrogen easily more than half the people now living would need to starve to death.)

The energy for this reaction comes from the use of dangerous natural gas (reformed with water to give hydrogen gas). According to the USGS the world produced 140 million metric tons of ammonia in 2016. The thermodynamic limit for this reaction is on the order of 20.9 GJ/ton, as of 2000, according to Smil's famous book on the topic, the industrial process's energy requirement had been reduced from 100 GJ/ton (dangerous coal based) in 1920 to 26 GJ/ton by the year 2000 (dangerous natural gas based.) (Smil, Enriching the Earth, MIT Press, 2001, Appendix K, Page 244.) It is difficult to imagine that an industrial process operating in 2000 at 80% thermodynamic efficiency has improved by all that much, but even it were operating at 100% efficiency, it would still represent a significant amount of energy. At 26 GJ/ton the demand to make 140 million tons of ammonia would be around 3.6 exajoules.

For comparison sake, all the world's solar and wind plants combined, the subject of so much delusional cheering, according to the 2017 World Energy Outlook, table 2.2, page 79 produced 9.4 exajoules of energy (out of 576 exajoules overall.)

However, much of the energy associated with ammonia production involves both heat and pressure to overcome the thermodynamic barrier of breaking the nitrogen-nitrogen triple bond in nitrogen gas. This bond is one of the strongest chemical bonds known, having a strength of 941 kJ/mol, (225 kcal/mol). (cf: Chirik et al, Nature Chemistry volume 2, pages 30–35 (2010))

Thus it was with interest that I came across a note in my email referring to recent calculations by the Dean of Engineering at Princeton University, Emily Carter, and one of her students that show that it is possible, based on computational chemistry determinations to photochemically lower the activation energy for the dissociation of nitrogen-nitrogen bonds:

New process could slash energy demands of fertilizer, nitrogen-based chemicals.

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Dr. Carter is one of the foremost computational chemists in the world, a leader in the development of what is known as "orbital-free density functional theory," a method of calculations to direct the discovery of new materials, catalysts and other molecules. While this sort of thing is somewhat esoteric, it is nonetheless extremely important to science and technology, and thus to modern human life.

It is difficult to predict how world changing scientific discoveries will prove to be; many seem to be earth shattering, but afterwards encounter difficulties that prove industrially insurmountable or simply get lost for a lack of funding by people who hate science, like, say, um Trump, Ryan and their league of exceedingly stupid people.

Nonetheless this discovery predicting a gold nanoparticle based catalysis could prove to be very important. (Perhaps scientists in less declining countries than the United States could take it up.)

Dr. Carter's scientific paper is open sourced and is here: Prediction of a low-temperature N2 dissociation catalyst exploiting near-IR–to–visible light nanoplasmonics (Martirez and Carter, Sci. Adv. 2017;3: eaao4710 22 December 2017)

Have a pleasant Sunday.








Little Wing.

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