CO₂ Reforming Of CH₄ Over Ni-based Catalysts With Time Of Flight Mass Spectrometry

CO₂ reforming of CH₄?CRM?is a process to produce syngas by making full use of two kinds of greenhouse gases,which is attracted by many researchers' attention.The catalyst is vital importance for reforming reaction.Currently,many researches on reforming catalyst are focused on Ni-based catalyst that is an ideal catalyst for its good catalytic activity and low cost.But it also has some problems like carbon deposition.It's believed that the reforming reaction mechanism is an important basis for improving catalysts and optimizing reaction process.In this paper,Ni/nano-SiO₂ with high activity was prepared.The reforming reaction was carried out in situ with time-of-flight mass spectrometry?TOF-MS?to make a comparison of catalysts performance.The activation of CH₄ and CO₂ were studied on a Ni/nano-Si O₂ and a composite catalyst with La₂O₃ added.TOF-MS was modified for detecting the reforming reaction on catalysts in situ.And a quantitative method was established for signals of mass spectrometry.The mass spectrometry signals were regulated by relative sensitivity factor,which could simplify process of analysis and comparison.The performance of Ni/nano-SiO₂,Ni/MgO and commercial Ni catalyst?Ni/Al₂O₃?in CRM were investigated by TOF-MS.The results indicated that Ni/nano-SiO₂ has the lowest starting temperature of reaction.But its activation of CO₂ is weak,which may cause carbon deposition.Experiments in fixed bed and thermogravimetric analysis were carried out.The results indicated that the Ni/nano-SiO₂ has the best activity in all of the catalysts,but has more serious carbon deposition and lower stability.In order to improve the ability of anti-carbon deposition,La₂O₃ was added into Ni/nano-SiO₂.The XRD results indicated that the addition of La₂O₃ improved the dispersion of Ni and reduced the size of Ni particles.The results of mass spectrometry indicated that the composite catalyst has better performance than Ni/nano-SiO₂,which has lower starting reaction temperature and higher activation of CO₂.Experiments in fixed bed and thermogravimetric analysis results also indicated that the composite catalyst has higher stability and anti-carbon deposition.The activation mechanisms of CH₄ and CO₂ on Ni/nano-SiO₂ and the composite catalyst were investigated by CH₄/CO₂ switch experiment.The results showed that CHx species would be produced on the surface of Ni/nano-SiO₂,which could react with CO₂ to product CO and H2.In the absence of CO₂,CHx could't dissociated rapidly for larger activation energy,and then covered active sites,resulting in inhibiting the dissociation of CH₄ after that.However,CO₂ could be activated on the surface of the composite catalyst,then formed active species that could be easier to react with CHx than CO₂,which was conducive to reducing carbon deposition.The CD₄/H2 isotope exchange experiment was carried out to study the dissociation process of CD₄ on Ni/nano-SiO₂.The results showed that CD₄ was firstly dissociated to be CD₃ and D.