The deep learning-based fault diagnosis approaches have shown great advantages in ensuring rotating machinery (RM) work normally and safely. However, in real industrial applications, due to the ...influence of speed fluctuation, the differences in distribution of training samples and testing samples are inevitable, which will greatly affect the diagnosis result of the model. In the article, a novel end-to-end method for the fault transfer diagnosis of RM under time-varying speeds, named semisupervised subdomain adaptation graph convolutional network (SSAGCN) is proposed by integrating SSA and GCN. To begin with, a feature extractor based on GCN is designed to obtain the transferable information of the source domain (SD) and target domain (TD) data. In addition, the closely watched fault diagnosis (FD) approach based on global domain shift and unsupervised domain adaptation is improved by employing an adaptive layer based on SSA to reduce the distribution difference of the same fault type in SD and TD. The proposed SSAGCN approach takes full advantage of the powerful capability of GCN in capturing the relationship between signals, and the excellent performance of SSA in the use of unlabeled samples and idle labeled samples, thus overcoming the distribution differences caused by speed fluctuation. Two experimental cases are carried out to prove its effectiveness under time-varying speeds, and their results indicate our presented SSAGCN approach can realize more excellent performance on diagnosis accuracy and model complexity compared with existing methods.
Selective electrocatalytic oxidation of alcohols to value‐added aldehydes has attracted increasing attention. However, due to its higher reactivity than alcohol, the aldehyde is easily over‐oxidized ...to acid in alkaline electrolytes. Herein we realize the selective electrooxidation of alcohol to aldehyde on NiO by tuning the local microenvironment to salt out the aldehyde from the reaction system. The origin of the high selectivity was found to be the inhibition of the hydration of aldehydes, which is the result of the decreased alkalinity and the increased cation and substrate concentration. This strategy could salt out the aldehyde at the gas|electrolyte interface from the electrooxidation of alcohol with 100 % selectivity and be easily extended to other selective oxidation reactions, such as 5‐hydroxymethyl furfural (HMF) to 2,5‐furandicarboxaldehyde (DFF) and amine to an imine.
Selective electrocatalytic oxidation of alcohols to aldehydes has significant challenges, for example, it cannot realize the preparation of aldehydes selectively in alkaline aqueous solutions. By tuning the local microenvironment over the electrocatalyst, and thus selectively salting‐out the aldehyde at the gas|electrolyte interface, the electrocatalytic synthesis of aldehydes was achieved in an efficient and green way.
Abstract
Alanine is widely employed for synthesizing polymers, pharmaceuticals, and agrochemicals. Electrocatalytic coupling of biomass molecules and waste nitrate is attractive for the nitrate ...removal and alanine production under ambient conditions. However, the reaction efficiency is relatively low due to the activation of the stable substrates, and the coupling of two reactive intermediates remains challenging. Herein, we realize the integrated tandem electrochemical‐chemical‐electochemical synthesis of alanine from the biomass‐derived pyruvic acid (PA) and waste nitrate (NO
3
−
) catalyzed by PdCu nano‐bead‐wires (PdCu NBWs). The overall reaction pathway is demonstrated as a multiple‐step catalytic cascade process via coupling the reactive intermediates NH
2
OH and PA on the catalyst surface. Interestingly, in this integrated tandem electrochemical‐chemical‐electrochemical catalytic cascade process, Cu facilitates the electrochemical reduction of nitrate to NH
2
OH intermediates, which chemically couple with PA to form the pyruvic oxime, and Pd promotes the electrochemical reduction of pyruvic oxime to the desirable alanine. This work provides a green strategy to convert waste NO
3
−
to wealth and enriches the substrate scope of renewable biomass feedstocks to produce high‐value amino acids.
The nitrogenous nucleophile electrooxidation reaction (NOR) plays a vital role in the degradation and transformation of available nitrogen. Focusing on the NOR mediated by the β‐Ni(OH)2 electrode, we ...decipher the transformation mechanism of the nitrogenous nucleophile. For the two‐step NOR, proton‐coupled electron transfer (PCET) is the bridge between electrocatalytic dehydrogenation from β‐Ni(OH)2 to β‐Ni(OH)O, and the spontaneous nucleophile dehydrogenative oxidation reaction. This theory can give a good explanation for hydrazine and primary amine oxidation reactions, but is insufficient for the urea oxidation reaction (UOR). Through operando tracing of bond rupture and formation processes during the UOR, as well as theoretical calculations, we propose a possible UOR mechanism whereby intramolecular coupling of the N−N bond, accompanied by PCET, hydration and rearrangement processes, results in high performance and ca. 100 % N2 selectivity. These discoveries clarify the evolution of nitrogenous molecules during the NOR, and they elucidate fundamental aspects of electrocatalysis involving nitrogen‐containing species.
During urea electrooxidation over a Ni(OH)2 electrode the dehydrogenation reaction from β‐Ni(OH)2 to β‐Ni(OH)O can lead to spontaneous urea dehydrogenation. Spontaneous intramolecular coupling of the N−N bond and hydration of urea dehydrogenation intermediates play important roles in the oxidation path from urea to N2 and CO2.
The nucleophile oxidation reaction (NOR) is of enormous significance for organic electrosynthesis and coupling for hydrogen generation. However, the nonuniform NOR mechanism limits its development. ...For the NOR, involving electrocatalysis and organic chemistry, both the electrochemical step and non‐electrochemical process should be taken into account. The NOR of nickel‐based hydroxides includes the electrogenerated dehydrogenation of the Ni2+–OH bond and a spontaneous non‐electrochemical process; the former determines the electrochemical activity, and the nucleophile oxidation pathway depends on the latter. Herein, the space‐confinement‐induced synthesis of Ni3Fe layered double hydroxide intercalated with single‐atom‐layer Pt nanosheets (Ni3Fe LDH‐Pt NS) is reported. The synergy of interlayer Pt nanosheets and multiple defects activates Ni–OH bonds, thus exhibiting an excellent NOR performance. The spontaneous non‐electrochemical steps of the NOR are revealed, such as proton‐coupled electron transfer (PCET; Ni3+–O + X–H = Ni2+–OH + X•), hydration, and rearrangement. Hence, the reaction pathway of the NOR is deciphered, which not only helps to perfect the NOR mechanism, but also provides inspiration for organic electrosynthesis.
The nucleophile oxidation reaction (NOR) is a complex reaction including electrochemical step and spontaneous non‐electrochemical process. The interlayer Pt nanosheets and multiple defects of Ni3Fe LDH‐Pt NS enable the activated Ni2+–OH to exhibit an excellent NOR activity. More importantly, spontaneous non‐electrochemical steps, including proton‐coupled electron transfer, hydration, and rearrangement, lead to diverse nucleophile dehydrogenation oxidation pathways of different NOR systems.
Synthesis of cyclohexanone oxime via the cyclohexanone‐hydroxylamine process is widespread in the caprolactam industry, which is an upstream industry for nylon‐6 production. However, there are two ...shortcomings in this process, harsh reaction conditions and the potential danger posed by explosive hydroxylamine. In this study, we presented a direct electrosynthesis of cyclohexanone oxime using nitrogen oxides and cyclohexanone, which eliminated the usage of hydroxylamine and demonstrated a green production of caprolactam. With the Fe electrocatalysts, a production rate of 55.9 g h−1 gcat−1 can be achieved in a flow cell with almost 100 % yield of cyclohexanone oxime. The high efficiency was attributed to their ability of accumulating adsorbed hydroxylamine and cyclohexanone. This study provides a theoretical basis for electrocatalyst design for C−N coupling reactions and illuminates the tantalizing possibility to upgrade the caprolactam industry towards safety and sustainability.
Towards efficient electrocatalysis of C−N coupling reactions, the accumulation of critical intermediates, i.e., N‐containing and C‐containing intermediates, must be facilitated. Taking the direct electrosynthesis of cyclohexanone oxime as an example, Fe can serve as an ideal electrode because it can accumulate adsorbed hydroxylamine and cyclohexanone, which is supported by DFT calculations and in situ characterizations.
Preventing the deactivation of noble metal-based catalysts due to self-oxidation and poisonous adsorption is a significant challenge in organic electro-oxidation. In this study, we employ a pulsed ...potential electrolysis strategy for the selective electrocatalytic oxidation of glycerol to glyceric acid over a Pt-based catalyst. In situ Fourier-transform infrared spectroscopy, quasi-in situ X-ray photoelectron spectroscopy, and finite element simulations reveal that the pulsed potential could tailor the catalyst's oxidation and surface micro-environment. This prevents the overaccumulation of poisoning intermediate species and frees up active sites for the re-adsorption of OH adsorbate and glycerol. The pulsed potential electrolysis strategy results in a higher glyceric acid selectivity (81.8%) than constant-potential electrocatalysis with 0.7 V
(37.8%). This work offers an efficient strategy to mitigate the deactivation of noble metal-based electrocatalysts.
The low-potential furfural oxidation reaction (FFOR) on a Cu-based electrocatalyst can produce H
at the anode, thereby providing a bipolar H
production system with an ultralow cell voltage. However, ...the intrinsic activity and stability of the Cu-based electrocatalyst for the FFOR remain unsatisfactory for practical applications. This study investigates the correlation between the valence state and the adsorption behavior of the Cu-based electrocatalyst in furfural oxidation. Cu
is the adsorption site with low intrinsic activity. Cu
, which exists in the form of Cu(OH)
in alkaline electrolytes, has no adsorption ability but can improve the performance of Cu
by promoting the adsorption of FF. Moreover, a mixed-valence Cu-based electrocatalyst (MV Cu) with high intrinsic activity and stability is prepared electrochemically. With the MV Cu catalyst, the assembled dual-side H
production electrolyzer has a low electricity requirement of only 0.24 kWh m
at an ultralow cell voltage of 0.3 V, and it exhibits sufficient stability. This study not only correlates the valence state with the adsorption behavior of the Cu-based electrocatalyst for the low-potential FFOR with anodic H
production but also reveals the mechanism of deactivation to provide design principles for Cu-based electrocatalysts with satisfactory stability.
5‐Hydroxymethylfurfural (HMF), one of the essential C6 biomass derivatives, has been deeply investigated in electrocatalytic reduction upgrading. Nevertheless, the high product selectivity and ...rational design strategy of electrocatalysts for electrocatalytic HMF reduction is still a challenge. Here, a high selective electro‐reduction of HMF to dimethylfuran (DMF) on palladium (Pd) single atom loaded on titanium dioxide (Pd SA/TiO2) via hydrogen spillover and adsorption configuration adjustment in neutral electrolytes is achieved. Combining density functional theory calculations and in situ characterization, it is revealed that Pd single atom could weaken the interaction between Pd atoms and adsorbed hydrogen (*H) to promote the *H spillover for increasing *H coverage on the surface and maintain the tilted adsorption configuration to activate C═O bond; thus the selectivity of DMF on Pd SA/TiO2 increases to 90.33%. Besides, it is elaborated that low *H coverage on TiO2 favors the formation of bis(hydroxymethyl)hydro‐furoin (BHH), and the flat adsorption configuration of HMF on Pd nanoparticles benefits to form 2,5‐dihydroxymethylfuran (DHMF). This work provides a promising approach for modifying electrocatalysts to realize the selective electroreduction of HMF to value‐added products.
Selective electrocatalytic 5‐hydroxymethylfurfural reduction reaction in neutral electrolytes to 2,5‐dihydroxymethylfuran is a challenging reaction. Loaded palladium (Pd) single atoms enable the adsorbed hydrogen (*H) spillover to increase the *H coverage on titanium dioxide (TiO2) and maintain the tilted configuration to activate the C═O bond, thus promoting selective electro‐reduction to 2,5‐dihydroxymethylfuran. Besides, the selective electro‐reduction to bis(hydroxymethyl)hydro‐furoin or 2,5‐dihydroxymethylfuran can also be achieved on TiO2 or Pd nanoparticles loaded on Vulcan‐XC72.
Abstract
Alanine is widely employed for synthesizing polymers, pharmaceuticals, and agrochemicals. Electrocatalytic coupling of biomass molecules and waste nitrate is attractive for the nitrate ...removal and alanine production under ambient conditions. However, the reaction efficiency is relatively low due to the activation of the stable substrates, and the coupling of two reactive intermediates remains challenging. Herein, we realize the integrated tandem electrochemical‐chemical‐electochemical synthesis of alanine from the biomass‐derived pyruvic acid (PA) and waste nitrate (NO
3
−
) catalyzed by PdCu nano‐bead‐wires (PdCu NBWs). The overall reaction pathway is demonstrated as a multiple‐step catalytic cascade process via coupling the reactive intermediates NH
2
OH and PA on the catalyst surface. Interestingly, in this integrated tandem electrochemical‐chemical‐electrochemical catalytic cascade process, Cu facilitates the electrochemical reduction of nitrate to NH
2
OH intermediates, which chemically couple with PA to form the pyruvic oxime, and Pd promotes the electrochemical reduction of pyruvic oxime to the desirable alanine. This work provides a green strategy to convert waste NO
3
−
to wealth and enriches the substrate scope of renewable biomass feedstocks to produce high‐value amino acids.
