| Concerns about the depletion of petroleum reserves and considering the chemical recycling of CO2to fuels/chemicals warrant particular attention for the dry reforming of methane (DRM) in recent years. DRM can convert both CH4and CO2into syngas that can be processed into liquid fuel, chemicals, or fertilizer agents, and also shows great potential for the applications in solar and nuclear energy storage due to its strong endothermicity (ΔH=247kJ mol"1). Although the noble metal-based catalysts are generally reported more active to reactant conversion and less sensitive to carbon deposition, their application is confined by high cost and limited availability. However, the major challenge of using Ni-based catalysts is the high thermodynamic potential to carbon deposition, which will not only induce the deactivation of catalysts, but also crush the catalysts pellets, increases the pressure drop, and even block the reactor. Thus, the goal of the present work is to develop the catalytic material and micro-structured reactor technology with high activity and enhanced carbon resistance for DRM.(1) Role of CeAlO3in Enhancement of Carbon Resistance of Ni/CeAlO3-A12O3Catalyst for DRMCe-promoted Ni/Al2O3(Ni/AlO) catalyst was prepared by stepwise incipient wetness impregnation method, and evaluated in a micro fixed bed reactor at atmosphere pressure.X-ray diffraction (XRD) employed to identify the bulk phases of the catalysts suggests that the Ce is existed in form of CeA103after reduction at1173K, and so is it at working condition. The results of XRD and transmission electron microscopy (TEM) demonstrate that Ni/CeA103-Al203(Ni/Ce-AlO) catalystexhibits a good thermal stability by suppressing the formation of NiAlO4), attenuating Ni sintering and preventing phase transition of the γ-AI2O3.Initial activity tests (within temperature of873～1173K and GHSV of 10,000～40,000mL h-1.gcat-1)and CH4temperature-programmed surface reaction (CH4一TPSR)experiments were carried out to study the effects of Ce-promotion on activity.The results indicate that the presence of CeAlo3has negligible influence on apparent initial activity.●During the longer-term tests for250h(1073K,20,000mL h-1gcat-1,atmosphere pressure) over Ni/Ce-AlO with different CeAlO3contents,the catalysts exhibited simiIar performance without appreciable deactivation, but the carbon content decreased from0.92gcar./gcat.. to0.29gcar./gcat. as the content of CeAlO3increased from0to15wt％. By inductively coupled plasma atomic emission spectrometry (ICP-AES),thermogravimetric analysis (TGA), XRD, scanning electron microscopy (SEM), TEM, and temperature-programmed experiments,we demonstrated that Ce in form of CeAlO3can readily inhibit the growth of graphitic carbon on nickel paticles over Ni/Ce-AlO catalysts for DRM reaction in a kinetic way, while the formation Of amorphous carbon is independent of the content Of CeAlO3phase.●According to the results of CO2temperature-prOgrammed surface reaction (CO2-TPSR) and ex-situ XRD, a model of DRM reaction and carbon deposition on Ni/AlO catalyst with or without CeAlO3was proposed: CeAlO3on catalyst can capture the CO2to form considerable carbonate species or active surface oxygen due to its reducibiIity. The gasification of isolated carbon atom at nickel-support boudary is so efficient that the carbon can be quickly converted to CO product, thus decreasing the possibility of graphene layer formationthereby suppressing the carbon deposition kinetically.(2) Microfibrous Structured Bed Reactor: A Demonstration on Process Intensification●Cu-Microfibrous entrapped Ni/AlO bed (Ni/AlO@Cu) was prepared through wet-lay paper making method,followed by sintering in a H2atmosphere. The catalytic activities of Ni/AlO@Cu, including a set of comparative beds, were evaluated for DRM reaction. The results demonstrate the enhancement of conversiOn arising from intensified transfer characteristics of Ni/AlO@Cu. The comparison between Ni/AlO@Cu and Ni/AlO packed bed (Ni/AlO@PB) shows that the rate of carbon formation in Ni/Al0@Cu was1.68xlO-3g h-1gcat-1, less than a half that (3.68×1-3g h-1gcat-1) in the Ni/A1O@PB, although both microfibrous bed and packed bed showed compatible conversion maintenance throughout the250h test. While the Ni/Ce-AlO@Cu composite bed exhibited better performance on carbon resistance (1.05×10-3g h-1gcat-1) during the1000h time on stream test.Computational fluid dynamics (CFD) code FLUENT was employed to simulate the DRM reaction inside the Ni/AlO@Cu and Ni/AlO@PB. The results clarify the thermal conductivity enhancement stemmed from such microfibrous entrapment technology enjoying high heat transfer, robust monolithic structure and unique form factors, By taking these desirable beneficial properties, significant improvement of the catalyst carbon resistance can be achieved along with an obvious promotion of the steady-state reactor conversion, compared to the packed bed with the same Ni/AlO catalyst under compatible reaction conditions. |
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