This work reports a process in which concentrated irradiation from a simulated solar source converts methane to high-value graphitic carbon and hydrogen gas. Methane flows within a photo-thermal reactor through the pores of a thin substrate irradiated by several thousand suns at the focal peak. The methane decomposes primarily into hydrogen while depositing highly graphitic carbon that grows conformally over ligaments in the porous substrate. The localized solar heating of the porous substrate serves to capture the solid carbon into a readily extractable and useful form while maintaining active deposition site density with persistent catalytic activity. Results indicate a strong temperature dependence with high decomposition occurring in the central heating zone with concentration factors and temperatures above 1000 suns and 1300 K, respectively. Even with a large flow area through regions of lower irradiation and temperature, methane conversion and hydrogen yields of approx. 70\% are achieved, and 58\% of the inlet carbon is captured in graphitic form.
We present a heterodyne terahertz spectrometry platform based on plasmonic photomixing, which enables the resolution of narrow spectral signatures of gases over a broad terahertz frequency range. This plasmonic heterodyne spectrometer replaces the terahertz mixer and local oscillator of conventional heterodyne spectrometers with a plasmonic photomixer and a heterodyning optical pump beam, respectively. The heterodyning optical pump beam is formed by two continuous-wave, wavelength-tunable lasers with a broadly tunable terahertz beat frequency. This broadly tunable terahertz beat frequency enables spectrometry over a broad bandwidth, which is not restricted by the bandwidth limitations of conventional terahertz mixers and local oscillators. We use this plasmonic heterodyne spectrometry platform to resolve the spectral signatures of ammonia over a 1-5 THz frequency range. THE MANUSCRIPTHeterodyne terahertz spectrometry is an attractive modality for gas sensing, because it can provide high spectral resolution for resolving narrow gas spectral lines [1][2][3][4][5][6]. It involves background radiation from a terahertz or blackbody source interacting with the gas under test. The radiation received by the heterodyne spectrometer carries the spectral signatures of the gas and is mixed with a terahertz local oscillator signal to downconvert the targeted terahertz spectral signature to an intermediate frequency (IF) signal in the radio frequency (RF) range. The downconverted spectrum is then resolved by backend IF electronics. Schottky diode, superconductor-insulator-superconductor (SIS), and hot electron bolometer (HEB) mixers are used for frequency-downconversion in conventional heterodyne terahertz spectrometers [6][7][8][9][10][11][12]. While conventional heterodyne terahertz spectrometers offer high spectral resolution and high sensitivity levels at cryogenic temperatures, their room temperature sensitivity and operation bandwidth are restricted by the sensitivity limitations of room-temperature terahertz mixers and frequency tunability constraints of terahertz local oscillators, respectively.To address these limitations, we recently introduced a heterodyne terahertz spectrometry scheme based on plasmonic photomixing [13][14][15][16][17][18][19][20]. By replacing the terahertz mixer and local oscillator of conventional heterodyne spectrometers with a plasmonic photomixer and a heterodyning optical pump beam, respectively, we demonstrated a heterodyne terahertz detector 2 with quantum-level sensitivities at room temperature and operation bandwidths exceeding 5 THz [21]. In this work, we use this plasmonic photomixer to resolve the spectral signatures of ammonia. Ammonia gas sensing is of interest for agriculture, combustion exhaust treatment, clinical breath analysis, and industrial process monitoring [22][23][24][25][26]. We chose ammonia for our first spectrometry measurements because its rotational spectra in the terahertz band provide comparable intensity to the strongest infrared vibrational bands. In addition, a...
This work reports a process in which concentrated irradiation from a simulated solar source converts methane to high-value graphitic carbon and hydrogen gas. Methane flows within a photo-thermal reactor through the pores of a thin substrate irradiated by several thousand suns at the focal peak. The methane decomposes primarily into hydrogen while depositing highly graphitic carbon that grows conformally over ligaments in the porous substrate. The localized solar heating of the porous substrate serves to capture the solid carbon into a readily extractable and useful form while maintaining active deposition site density with persistent catalytic activity. Results indicate a strong temperature dependence with high decomposition occurring in the central heating zone with concentration factors and temperatures above 1000 suns and 1300 K, respectively. Even with a large flow area through regions of lower irradiation and temperature, methane conversion and hydrogen yields of approx. 70\% are achieved, and 58\% of the inlet carbon is captured in graphitic form.
A multi-MHz laser absorption sensor at 777.2 nm ( 12 , 863 c m − 1 ) is developed for simultaneous sensing of (1) O ( 5 S 0 ) number density, (2) electron number density, and (3) translational temperature at conditions relevant to high-speed entry conditions and molecular dissociation. This sensor leverages a bias tee circuit with a distributed feedback diode laser and an optimization of the laser current modulation waveform to enable temporal resolution of sub-microsecond kinetics at electronvolt temperatures. In shock-heated O 2 , the precision of the temperature measurement is tested at 5 MHz and is found to be within ± 5 % from 6000 to 12,000 K at pressures from 0.1 to 1 atm. The present sensor is also demonstrated in a CO:Ar mixture, in parallel with a diagnostic for CO rovibrational temperature, providing an additional validation across 7500–9700 K during molecular dissociation. A demonstration of the electron number density measurement near 11,000 K is performed and compared to a simplified model of ionization. Finally, as an illustration of the utility of this high-speed diagnostic, the measurement of the heavy particle excitation rate of O ( 5 S 0 ) is extended beyond the temperatures available in the literature and is found to be well represented by k ( 3 P → 5 S 0 ) = 2.7 × 10 − 14 T 0.5 exp ( − 1.428 × 10 4 / T ) c m 3 ⋅ s − 1 from 5400 to 12,200 K.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.