美國萊斯大學(xué)的科學(xué)家們發(fā)明了一種將氨轉(zhuǎn)化為氫的新方法

這項(xiàng)研究遵循政府和行業(yè)投資，為不會導(dǎo)致溫室效應(yīng)的無碳液氨燃料創(chuàng)建基礎(chǔ)設(shè)施和市場

氨氣仍然是相當(dāng)有害的氣體，但它的點(diǎn)火和快速燃燒是可以忽略不計(jì)的

據(jù)油價(jià)網(wǎng)報(bào)道，美國萊斯大學(xué)(Rice University)的科學(xué)家們?nèi)涨鞍l(fā)明了一種光活化催化劑，可以只使用廉價(jià)的原材料就能有效地將氨氣轉(zhuǎn)化為清潔燃燒的氫氣。這個(gè)設(shè)計(jì)是一種光激活納米材料，可將氨氣轉(zhuǎn)化為清潔燃燒的氫氣。

這項(xiàng)工作是萊斯大學(xué)納米光子學(xué)實(shí)驗(yàn)室、Syzygy等離子體子學(xué)公司和普林斯頓大學(xué)Andlinger能源與環(huán)境中心的一個(gè)合作項(xiàng)目。該研究報(bào)告已發(fā)表在《科學(xué)》雜志上。

在這項(xiàng)研究啟動之前，美國政府和行業(yè)投資建立了基礎(chǔ)設(shè)施和市場，以生產(chǎn)不會導(dǎo)致溫室效應(yīng)的無碳液態(tài)氨燃料。液態(tài)氨易于運(yùn)輸，每個(gè)分子含有1個(gè)氮原子和3個(gè)氫原子，能量巨大。新的催化劑將這些分子分解成氫氣(一種清潔的燃料)和氮?dú)?地球大氣中最大的成分)。與傳統(tǒng)催化劑不同的是，它不需要熱量。相反，它從光中收集能量，無論是陽光還是節(jié)能的LED。

化學(xué)反應(yīng)的速度通常隨著溫度的升高而加快，一個(gè)多世紀(jì)以來，化學(xué)品生產(chǎn)商一直在利用這一點(diǎn)，在工業(yè)規(guī)模上加熱。燃燒化石燃料將大型反應(yīng)容器的溫度提高數(shù)百或數(shù)千度會產(chǎn)生巨大的碳足跡。化學(xué)品生產(chǎn)商每年還在熱催化劑上花費(fèi)數(shù)十億美元，這種材料不發(fā)生反應(yīng)，但在強(qiáng)烈加熱下會加速反應(yīng)。

這項(xiàng)研究的合著者、萊斯大學(xué)的內(nèi)奧米·哈拉斯指出：“像鐵這樣的過渡金屬通常是較差的熱催化劑，這項(xiàng)工作表明它們可以成為高效的等離子體光催化劑。這也證明了光催化可以用廉價(jià)的LED光子源有效地進(jìn)行。” 

萊斯大學(xué)研究報(bào)告的合著者彼得·諾德蘭德補(bǔ)充說：“這一發(fā)現(xiàn)為可持續(xù)的、低成本的氫氣鋪平了道路，這種氫氣可以在當(dāng)?shù)厣a(chǎn)，而不是在大型集中式工廠生產(chǎn)。” 

最好的熱催化劑是由鉑和相關(guān)貴金屬如鈀、銠和釕制成的。 哈拉斯和諾德蘭德花了數(shù)年時(shí)間開發(fā)光激活或等離子體金屬納米顆粒。 其中最好的也通常是由銀和金等貴金屬制成的。

2011年，他們發(fā)現(xiàn)了等離子體粒子，這種粒子會釋放出短命的高能電子，稱為“熱載流子”。2016年，他們發(fā)現(xiàn)熱載流子發(fā)電機(jī)可以與催化粒子結(jié)合，產(chǎn)生混合“天線反應(yīng)器”，其中一部分從光中收集能量，另一部分利用能量以外科手術(shù)般的精度驅(qū)動化學(xué)反應(yīng)。

哈拉斯、諾德蘭德、他們的學(xué)生和合作者多年來一直致力于為天線反應(yīng)器的能量收集部分和反應(yīng)加速部分尋找非貴金屬替代品。這項(xiàng)新研究是這項(xiàng)工作的高潮。在這篇文章中，哈拉斯、諾德倫德、萊斯大學(xué)校友侯賽因· 羅巴塔茲、普林斯頓大學(xué)工程師兼物理化學(xué)家艾米麗·卡特等人展示了由銅和鐵制成的天線反應(yīng)器粒子在轉(zhuǎn)化氨氣方面非常高效。粒子的銅能量收集部分從可見光中獲取能量。

Robatjazi是哈拉斯研究小組的博士校友，現(xiàn)在是總部位于休斯敦的光催化劑研發(fā)公司Syzygy Plasmonics的首席科學(xué)家，他解釋說，在沒有光的情況下，銅-鐵催化劑表現(xiàn)出比銅-釕催化劑低300倍的反應(yīng)活性，這并不奇怪，因?yàn)獒懯且环N反應(yīng)更好的熱催化劑。在光照下，銅-鐵的效率和反應(yīng)活性與銅-釕的效率和反應(yīng)活性相似并具有可比性。

Syzygy Plasmonics公司已經(jīng)獲得了萊斯大學(xué)的天線反應(yīng)器技術(shù)的許可，該研究還包括在該公司的商用LED動力反應(yīng)器中對催化劑進(jìn)行大規(guī)模測試。在萊斯大學(xué)的實(shí)驗(yàn)室測試中，用激光照亮了銅鐵催化劑。Syzygy Plasmonics公司的測試表明，催化劑在LED照明和比實(shí)驗(yàn)室設(shè)置大500倍的規(guī)模下仍然保持其效率。

哈拉斯說：“這是科學(xué)文獻(xiàn)中第一份表明LED光催化可以從氨氣中產(chǎn)生克級數(shù)量的氫氣的報(bào)告。”“這為完全取代等離子體光催化中的貴金屬打開了大門。”

卡特補(bǔ)充說：“鑒于等離子體天線反應(yīng)器光催化劑在顯著減少化學(xué)部門碳排放方面的潛力，它們值得進(jìn)一步研究。”“這些結(jié)果是一個(gè)很好的激勵(lì)因素。他們認(rèn)為，充足的金屬的其他組合很可能被用作廣泛化學(xué)反應(yīng)的低成本催化劑。” 

有人可能會認(rèn)為，氫氣運(yùn)輸和儲存解決方案的大門很快就會打開。對于大多數(shù)人來說，氫氣作為運(yùn)輸燃料，便攜性和安全性更高。

氨氣仍然是相當(dāng)有害的氣體，但它的點(diǎn)火和快速燃燒可以忽略不計(jì)。氨氣也是氫氣的非加壓載體。氨氣確實(shí)有一種非常強(qiáng)烈的氣味。總而言之，作為一種實(shí)用的氫氣載體，它是相當(dāng)不錯(cuò)的。

還有一些問題，比如需要多少光能來驅(qū)動一輛汽車。擴(kuò)大測試正在進(jìn)行中。然后，人們會想知道如何消除氮?dú)猓约耙阅撤N方式將氮?dú)饣螂p氮分子排放回大氣中是否會造成能源成本。

李峻 編譯自 油價(jià)網(wǎng)

原文如下：

Scientist Invent New Way To Convert Ammonia Into Hydrogen

·     Rice University scientists have invented a new way to convert ammonia into hydrogen.

·     The research follows government and industry investment to create infrastructure and markets for carbon-free liquid ammonia fuel that will not contribute to greenhouse warming.

·     Ammonia is still fairly noxious, but its ignition and rapid combustion are negligible

Rice University scientists have invented a light-activated catalyst that efficiently converts ammonia into clean-burning hydrogen using only inexpensive raw materials. The design is a light-activated nanomaterial to convert the ammonia into clean-burning hydrogen fuel.

The effort is a collaborative project from Rice’s Laboratory for Nanophotonics, Syzygy Plasmonics Inc. and Princeton University’s Andlinger Center for Energy and the Environment. The research report has been published in the journal Science.

The research follows government and industry investment to create infrastructure and markets for carbon-free liquid ammonia fuel that will not contribute to greenhouse warming. Liquid ammonia is easy to transport and packs a lot of energy, with one nitrogen and three hydrogen atoms per molecule. The new catalyst breaks those molecules into hydrogen gas, a clean-burning fuel, and nitrogen gas, the largest component of Earth’s atmosphere. And unlike traditional catalysts, it doesn’t require heat. Instead, it harvests energy from light, either sunlight or energy-stingy LEDs.

The pace of chemical reactions typically increases with temperature, and chemical producers have capitalized on this for more than a century by applying heat on an industrial scale. The burning of fossil fuels to raise the temperature of large reaction vessels by hundreds or thousands of degrees results in an enormous carbon footprint. Chemical producers also spend billions of dollars each year on thermocatalysts – materials that don’t react but further speed reactions under intense heating.

Study co-author Naomi Halas of Rice noted, “Transition metals like iron are typically poor thermocatalysts, This work shows they can be efficient plasmonic photocatalysts. It also demonstrates that photocatalysis can be efficiently performed with inexpensive LED photon sources.”

Rice co-author Peter Nordlander added, “This discovery paves the way for sustainable, low-cost hydrogen that could be produced locally rather than in massive centralized plants.”

The best thermocatalysts are made from platinum and related precious metals like palladium, rhodium and ruthenium. Halas and Nordlander spent years developing light-activated, or plasmonic, metal nanoparticles. The best of these are also typically made with precious metals like silver and gold.

Following their 2011 discovery of plasmonic particles that give off short-lived, high-energy electrons called “hot carriers,” they discovered in 2016 that hot-carrier generators could be married with catalytic particles to produce hybrid “antenna-reactors,” where one part harvested energy from light and the other part used the energy to drive chemical reactions with surgical precision.

Halas, Nordlander, their students and collaborators have worked for years to find non-precious metal alternatives for both the energy-harvesting and reaction-speeding halves of antenna reactors. The new study is a culmination of that work. In it, Halas, Nordlander, Rice alumnus Hossein Robatjazi, Princeton engineer and physical chemist Emily Carter, and others show that antenna-reactor particles made of copper and iron are highly efficient at converting ammonia. The copper, energy-harvesting piece of the particles captures energy from visible light.

Robatjazi, a Ph.D. alumnus from Halas’ research group who is now chief scientist at Houston-based Syzygy Plasmonics explained, “In the absence of light, the copper-iron catalyst exhibited about 300 times lower reactivity than copper-ruthenium catalysts, which is not surprising given that ruthenium is a better thermocatalyst for this reaction. Under illumination, the copper-iron showed efficiencies and reactivities that were similar to and comparable with those of copper-ruthenium.

Syzygy has licensed Rice’s antenna-reactor technology, and the study included scaled-up tests of the catalyst in the company’s commercially available, LED-powered reactors. In laboratory tests at Rice, the copper-iron catalysts had been illuminated with lasers. The Syzygy tests showed the catalysts retained their efficiency under LED illumination and at a scale 500 times larger than lab setup.

“This is the first report in the scientific literature to show that photocatalysis with LEDs can produce gram-scale quantities of hydrogen gas from ammonia,” Halas said. “This opens the door to entirely replace precious metals in plasmonic photocatalysis.”

“Given their potential for significantly reducing chemical sector carbon emissions, plasmonic antenna-reactor photocatalysts are worthy of further study,” Carter added. “These results are a great motivator. They suggest it is likely that other combinations of abundant metals could be used as cost-effective catalysts for a wide range of chemical reactions.”

One might think the door could be open soon for the hydrogen transport and storage solution. For most folks looking at hydrogen for a transport fuel, portability, and lots more safety, ammonia containment offers a huge leap forward.

Ammonia is still fairly noxious, but its ignition and rapid combustion are negligible. It is also a non pressurized carrier for hydrogen. It does have a very strong odor, giving some warning of its escape. All in all, as a practical hydrogen carrier, its pretty good.

There are some questions like just how much light energy is needed to say, power an automobile. The scale up testing is underway. Then one wonders how to dispense with the nitrogen and if there is an energy cost as well to venting somehow a N2 or di-nitrogen molecule back into the atmosphere harmlessly.

We’re going to be watching for more on this.