Research On Laser-driven Dry Reforming Of Methane And Bio-nitrogen Resource Utilization

The effective use of carbon and nitrogen resources is of unprecedented importance to solve the current environmental problems and energy crisis.Carbon dioxide（CO₂）and methane（CH₄）are not only typical greenhouse gases,but also important carbon-containing resources.Catalytic dry reforming of methane（DRM）offers an environmentally friendly and viable route for large-scale greenhouse gases utilization（CH₄+CO₂=2 CO+2 H₂）.However,harsh reaction conditions of thermocatalysis and the limited efficiency of photothermal catalysis hinder the development of DRM technology.Meanwhile,as a vital chemical,ammonia（NH₃）plays an irreplaceable role in many fields,such as chemical synthesis and energy storage.Due to the high dissociation energy of the N≡N bond(945 k J mol^-1),the process of ammonia synthesis from N₂ still needs to be solved with high energy consumption and low yield.In response to the above two thermodynamically unfavorable technical challenges,researchers have made a lot of attempts in thermal catalysis,photocatalysis,electrocatalysis and other technical routes.This paper explored the unique mechanism of short-pulse laser-matter interactions.The pulsed laser was used as the sole energy input to drive thermodynamically unfavorable reactions,and furthermore,a laser-driven pyrolysis system and a laser-catalysis system were constructed.Laser-driven pyrolysis of biomass under mild conditions for large-scale ammonia synthesis was achieved by the localized very fast thermal effect of laser action on biomass.Based on a deeper understanding of laser-induced thermal effect,this work further investigated laser-induced plasma effect and achieved significant enhancement of molybdenum carbide-catalyzed DRM by laser-induced thermal and plasma effects.The main research contents of this paper are as follows:（1）Laser-driven biomass pyrolysis for ammonia synthesis was constructed to take advantage of the unique thermal effect of pulsed laser action on biomass.The local-transient thermal effect induced by the pulsed laser can recognize the biological nitrogen resources conversion,such as cheap and plentiful yeasts,into small gaseous molecules and thus spectacular ammonia production rate(up to 260.4 mg h^-1),achieving an order of magnitude higher catalytic activity than thermochemical ammonia synthesis.Simultaneously,the tiny hot point generated by low-energy laser（20 W）guarantees the whole ammonia synthesis reaction system is in a mild environment of low temperature and normal pressure.Additionally,the remaining solid residue after laser-driven pyrolysis also can be further exploited as a highly active catalyst for electrocatalytic nitrate reduction reaction（NIRR）.（2）A laser-catalytic DRM system was constructed by coupling laser-induced thermal effects with laser-induced plasma using a nanosecond pulsed laser at a wavelength of 1064nm.The 16 W pulsed laser as a low energy source combined with cheap and simple Mo₂C as catalyst open a novel avenue for DRM under mild reaction conditions.In the laser-catalytic DRM process,the pulsed laser can simultaneously induce the localized high temperature and^*CH plasma on the surface of Mo₂C which accelerate the DRM reaction activity.It is important that,the pulsed laser directly realizes^*CH plasma from CH₄ via thermal ionization and cascade ionization mechanism,which avoids the step-by-step dehydrogenation of CH₄and then comprehensively breaks the rate-limiting step of methane cracking.In addition,the C*-O*balanced environment produced from CH₄ cracking by pulsed laser inhibits the deactivation of Mo₂C catalyst by excessive oxidation of CO₂.The pulsed laser-catalyzed DRM achieved the highest mass activity(yield of H₂:14300.8 mmol h^-1 g^-1,yield of CO14949.9 mmol h^-1 g^-1)reported so far with 0.48 mg catalyst.Herein,the proposed laser-catalytic DRM process is of great significance for broadening the research perspectives of photothermal catalytic systems,which circumvents the high energy consumption of external heating sources.