Visible light-enhanced photothermal CO2 hydrogenation over Pt/Al2O3 catalyst

Light illumination has been widely used to promote activity and selectivity of traditional thermal catalysts. Nevertheless, the role of light irradiation during catalytic reactions is not well understood. In this work, Pt/Al2 O3 prepared by wet impregnation was used for photothermal CO2 hydrogenation, and it showed a photothermal effect. Hence, operando diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations were conducted on Pt/Al2 O3 to gain insights into the reaction mechanism. The results indicated that CO desorption from Pt sites including step sites(Ptstep) or/and terrace site(Ptterrace) is an important step during CO2 hydrogenation to free the active Pt sites. Notably, visible light illumination and temperature affected the CO desorption in different ways. The calculated adsorption energy of CO on Ptstep and Ptterrace sites was-1.24 and-1.43 e V, respectively. Hence, CO is more strongly bound to the Ptstep sites. During heating in the dark, CO preferentially desorbs from the Ptterrace site. However, the additional light irradiation facilitates transfer of CO from the Ptstep to Ptterrace sites and its subsequent desorption from the Ptterrace sites, thus promoting the CO2 hydrogenation.

High-dimensional frequency conversion in a hot atomic system

One of the major difficulties in realizing a high-dimensional frequency converter for conventional optical vortex(COV)modes stems from the difference in ring diameter of the COV modes with different topological charge numbers l.Here,we implement a high-dimensional frequency converter for perfect optical vortex(POV)modes with invariant sizes by way of the four-wave mixing(FWM)process using Bessel–Gaussian beams instead of Laguerre–Gaussian beams.The measured conversion efficiency from 1530 to 795 nm is independent of l at least in subspace l∈{-6,………,6},and the achieved conversion fidelities for two-dimensional(2D)superposed POV states exceed 97%.We further realize the frequency conversion of 3D,5D,and 7D superposition states with fidelities as high as 96.70%,89.16%,and 88.68%,respectively.The proposed scheme is implemented in hot atomic vapor.It is also compatible with the cold atomic system and may find applications in high-capacity and long-distance quantum communication.

Promotion of photocatalytic steam reforming of methane over Ag^0/Ag^+-SrTiO3

Methane(CH4)is not only used as a fuel but also as a promising clean energy source for hydrogen generation.The steam reforming of CH4(SRM)using photocatalysts can realize the production of syngas(CO+H2)with low energy consumption.In this work,Ag0/Ag+-loaded SrTi03 nanocomposites were successfully prepared through a photodeposition method.When the loading amount of Ag is 0.5 mol%,the atom ratio of Ag+to Ag0 was found to be 51:49.In this case,a synergistic effect of Ago and Ag+was observed,in which Ago was proposed to improve the adsorption of H2 O to produce hydroxyl radicals and enhance the utilization of light energy as well as the separation of charge carriers.Meanwhile,Ag0 was regarded as the reduction reaction site with the function of an electron trapping agent.In addition,Ag+adsorbed the CH4 molecules and acted as the oxidation reaction sites in the process of photocatalytic SRM to further promote electron-hole separation.As a result,0.5 mol%Ag-SrTi03 exhibited enhancement of photocatalytic activity for SRM with the highest CO production rate of 4.3μmol g-1 h-1,which is ca.5 times higher than that of pure SrTi03.This work provides a facile route to fabricate nanocomposite with cocatalyst featuring different functions in promoting photocatalytic activity for SRM.

Numerical modeling of a linear photonic system for accurate and efficient time-domain simulations

In this paper, a novel modeling and simulation method for general linear, time-invariant, passive photonic devices and circuits is proposed. This technique, starting from the scattering parameters of the photonic system under study, builds a baseband equivalent state-space model that splits the optical carrier frequency and operates at baseband, thereby significantly reducing the modeling and simulation complexity without losing accuracy.Indeed, it is possible to analytically reconstruct the port signals of the photonic system under study starting from the time-domain simulation of the corresponding baseband equivalent model. However, such equivalent models are complex-valued systems and, in this scenario, the conventional passivity constraints are not applicable anymore. Hence, the passivity constraints for scattering parameters and state-space models of baseband equivalent systems are presented, which are essential for time-domain simulations. Three suitable examples demonstrate the feasibility, accuracy, and efficiency of the proposed method.

Time-domain compact macromodeling of linear photonic circuits via complex vector fitting

In this paper, a novel baseband macromodeling framework for linear passive photonic circuits is proposed, which is able to build accurate and compact models while taking into account the nonidealities,such as higher order dispersion and wavelength-dependent losses of the circuits. Compared to a previous modeling method based on the vector fitting algorithm, the proposed modeling approach introduces a novel complex vector fitting technique. It can generate a half-size state-space model for the same applications, thereby achieving a major improvement in efficiency of the time-domain simulations. The proposed modeling framework requires only measured or simulated scattering parameters as input,which are widely used to represent linear and passive systems. Three photonic circuits are studied to demonstrate the accuracy and efficiency of the proposed technique.