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Induction Heating: An Enabling Technology for the Heat Management in Catalytic Processes
No full textThis perspective illustrates the electromagnetic induction heating technology for a rational heat control in catalytic heterogeneous processes. It mainly focuses on the remarkable advantages of this approach in terms of process intensification, energy efficiency, reactor setup simplification, and safety issues coming from the use of radio frequency heated susceptors/catalysts in fixed-bed reactors under flow operational conditions. It is a real enabling technology that allows a catalytic process to go beyond reactor bounds, reducing inefficient energy transfer issues and heat dissipation phenomena while improving reactor hydrodynamics. Hence, it allows pushing catalytic processes to the limits of their kinetics. Undoubtedly, inductive heating represents a twist in performing catalysis. Indeed, it offers unique solutions to overcome heat transfer limitations (i.e. slow heating/cooling rates, nonuniform heating environments, low energy efficiency) to those endo- and exothermic catalytic transformations that make use of conventional heating methodologies
Direct Methane Conversion under Mild Condition by Thermo-, Electro-, or Photocatalysis
No full textDirect conversion of earth-abundant methane into value-added chemicals under mild conditions is an attractive technology in response to the increasing industrial demand of feedstocks and worldwide appeal of energy conservation. Exploring advanced low-temperature C-H activation catalysts and reaction systems is the key to converting methane in a direct and mild manner. The recently developed reaction processes operated at low-temperature thermocatalysis systems or driven in electro- and photocatalysis systems shine light on the way to achieve efficient methane conversion with much economical energy input. In this review, we summarize the typical catalytic processes employed in these reaction systems and in particular highlight the potential heterogeneous catalysts with noteworthy C-H activation performance. We also present the progress along with our perspectives on catalyst design, theoretical simulations, the choice of reaction condition, and the method of reaction product analysis to encourage more viable technology for low-temperature methane conversion in the future
Triplet Sensitization by "Self-Trapped" Excitons of Nontoxic CuInS2 Nanocrystals for Efficient Photon Upconversion
No full textTriplet energy transfer (TET) from semiconductor nanocrystals (NCs) has recently emerged as a new triplet sensitization paradigm. It remains unclear how trap states pervasive in NCs influence TET or whether trapped excitons can undergo efficient TET. Here we partially address this issue by studying TET from CuInS2 NCs as a model system because their photogenerated excitons are known to be "self-trapped" due to hole localization to intragap Cu states. We found that, thanks to the long lifetime (209 +/- 17 ns) of self-trapped excitons, they could be extracted with an efficiency of similar to 92.3% by surface-anchored anthracene despite that the TET rate was relatively slow (57.1 +/- 1.7 mu s(-1)). We further leveraged this efficient sensitization to achieve triplet-triplet-annihilation photon upconversion (TTA-UC) with a quantum yield of 18.6 +/- 0.3%. Thus, this study not only demonstrates trapped excitons can undergo efficient TET as well, but also presents the first TTA-UC system sensitized by nontoxic NCs which is important for the real-life application of this technique
Ethanol and Acetaldehyde Decomposition on Co(0001): The Effect of Hydrogen Atom on C-O Bond Scission
No full textFischer-Tropsch synthesis (FTS) with Co-based catalysts has attracted renewed interest in recent years due to its potential applications to produce transportation fuels. However, experimental investigations about the FT mechanism at the atomic level, especially for the essential C-O bond scission step, are rarely carried out. Using the temperature-programmed desorption method, we have investigated the mechanism of C-O bond scission in the decomposition of ethanol (C2H5OH) and acetaldehyde (CH3CHO). We have clearly found that the H atom attached to the C-end of the CO molecule is significant for C-O bond scission accompanied by CH3 at the C-end. Otherwise, C-C bond scission will occur facilely if only a CH3 group is attached to the C-end of the CO molecule. These results indicate that CH3CHO may be an important intermediate in FTS for C-O bond scission to produce C2Hx or for C-2+( )oxygenate production. Moreover, the H atoms on the Co(0001) surface could largely inhibit the dehydrogenation of the H atom at the C-end of CO, leading to an enhancement of C-O bond scission. The results for the first time demonstrate that, except the CH3 radical at the C-end of the CO molecule, an additional H atom at the C-end of the CO molecule and the surface H atoms play vital roles in promoting the C-O bond scission in the FT process as well
Two-layer Gaussian-based MCTDH study of the S-1 <- S-0 vibronic absorption spectrum of formaldehyde using multiplicative neural network potentials
No full textThe absorption spectrum of the vibronically allowed S-1((1)A(2)) <- S-0((1)A(1)) transition of formaldehyde is computed by combining multiplicative neural network (NN) potential surface fits, based on multireference electronic structure data, with the two-layer Gaussian-based multiconfiguration time-dependent Hartree (2L-GMCTDH) method. The NN potential surface fit avoids the local harmonic approximation for the evaluation of the potential energy matrix elements. Importantly, the NN surface can be constructed so as to be physically well-behaved outside the domain spanned by the ab initio data points. A comparison with experimental results shows spectroscopic accuracy of the converged surface and 2L-GMCTDH quantum dynamics. Published under license by AIP Publishing
Revealing the Highly Catalytic Performance of Spinel CoMn2O4 for Toluene Oxidation: Involvement and Replenishment of Oxygen Species Using In Situ Designed-TP Techniques
No full textThe catalytic oxidation of toluene to CO2 and H2O over nanoflower spinel CoMn2O4, synthesized by the oxalic acid sol-gel method has been investigated, and it demonstrates lower activation energy (35.5 kJ/mol) for toluene oxidation compared with that using the metal oxides (Co3O4, MnOx and Co3O4/MnOx), which shows nearly 100% conversion of toluene at 220 degrees C in the presence or absence of water vapor (2.0 vol %). Compared with the metal oxides (Co3O4/MnO MnOx, and Co3O4), the obtained spinel CoMn2O4 has a larger surface area, rich cationic vacancy, and high mobility of oxygen species, which are the reasons for its high activity for toluene oxidation. The different oxygen species shows the different role in VOCs oxidation, and the in situ designed-TP techniques are conducted to investigate the involvement of surface lattice oxygen, bulk lattice oxygen, and gaseous oxygen in catalytic oxidation of toluene over the spinel CoMn2O4 and Co3O4/MnOx catalysts. For spinel CoMn2O4, the surface lattice oxygen is the reactive oxygen species, which first induces the catalytic reaction. Furthermore, the gaseous oxygen moves to the bulk phase lattice and then migrates to the surface to form the surface lattice oxygen, which is different from the mixed-metal oxides Co3O4/MnOx that dissociates and activates gaseous oxygen only on the surface of the catalyst and requires a higher temperature. In addition, it is found that the toluene oxidation occurs via the benzyl alcohol benzoate anhydride acetate reaction pathway over spinel CoMn2O4, and the conversion of the surface anhydride is the rate-controlling step, especially at 200-210 degrees C, which is also different from the mixed-metal oxides Co3O4/MnOx, These results could provide a considerable experimental basis for understanding the mechanism by which oxygen species participate in toluene oxidation