Preparation,Characterization Of Highly Dispersed Anti-Sintered Ni/SiO₂ Catalysts And Their DRM Reaction Catalytic Performance

Dry reforming of methane?DRM?reaction attracts people's attention since its conducive to the rational use of natural resources,advantages of reducing carbon waste and greenhouse e:ffect.The main reasons stand in the way of industrial application of DRM is the difficult to find a highly efficient and stable catalyst.There are two main problems for the current load type Ni/SiO₂ catalyst,one is the sintering of Ni particles,the other one is carbon deposition.The first part of this dissertation we study the dispersion and catalytic activity of the load type Ni/SiO₂ catalysts prepared by different prescursors;We focus on the study of preparation mechanism about nano Ni/SiO₂ catalyst prepared by Ni?acac?₂ prescursor;The second part of this article we preliminarily explored the effect and modification mechanism of ammonia modified loading Ni/SiO₂ catalyst.The main results are summarized as follows:A series of Ni/SiO₂ catalysts were prepared by different precursors?Ni?acac?₂,Ni3?C6H5O7?2,Ni?CH₃C00?2·4H₂O,Ni?NO3?2·6H₂O,NiCl2·6H₂O?.Catalyst prepared by Ni?acac?₂ has better catalytic performance in DRM.We characterized the structure and particle size of the catalysts by XRD,characterized particle size by TEM,explored the combination between SiO₂ and Ni by H₂-TPR,characterized carbon deposition by TG and TPO.It indicates that Ni/SiO₂ catalyst prepared by Ni?acac?₂ has better dispersion,more closely relationship with SiO₂,less carbon deposition after DRM reaction,better anti-sinter resistance.The catalyst prepared by Ni?acac?₂ showed good catalytic performance and stability for DRM reaction within 280 h,the CH4 conversion was kept at?83%,the CO₂ conversion was maintained at?90%,the yield of CO and H₂ were kept at?87%and-86%,the carbon balance maintained at?100%.On this basis a series of Ni/SiO₂ catalysts with different Niwt%were prepared by Ni?acac?₂.The BET test show that Ni/SiO₂ catalysts have smaller specific surface area and pore volume than supporter SiO₂;5wt%Ni/SiO₂ catalyst prepared by Ni?acac?₂ was high resistant to aggregate of Ni particles.The size and dispersion of Ni particles were still maintain well?<5 nn?even after calcined at 900 ? for 2 h or calcined at 800 ? for 20 h;Analogy our groups previous conclusion 9wt%Pd/SiO₂ is the biggest monolayer coverage of Pd?acac?₂ on SiO₂ we caculate the biggest monolayer coverage of Ni?acac?₂ on SiO₂ is 7wt%.In-situ IR characterization of catalysts prepared by Ni?acac?₂ with different Ni loading show the sharp band?3737 cm-1?belongs to free silanol group decreases significantly in intensity with the increase of Ni?acac?₂ loading,whereas those of the hydrogen bonded OH species?3000-3800 cm-1?increase in intensity.This result indicates that the organic group of Ni?acac?₂ interacts with free silanol group of SiO₂ surface through hydrogen bond.As long as the loading of Ni?acac?₂ lower than the limitation of monolayer?7wt%Ni/SiO₂?the Ni particles will uniformly disperse on the surface of SiO₂.TEM and H₂-TPR characterization of catalysts prepared by Ni?acac?₂ with different Ni loading show the paticle size of Ni maintain small and the relationship with supported SiO₂ were more closely when Ni loading was below 7wt%.NH₃·H₂O can increase the anti-sinter resistance,dispersion of Ni particles,catalytic performance of DRM for catalysts prepared by Ni?NO3?2·6H₂O.The results of TG and in situ IR show that Ni?NO3?2·6H₂O and ammonia form coordination complex when co-impregnation which can promote the dispersion of nickel on supporter;Characterization of BET,in situ IR and conventional IR show that ammonia affects the surface Si-OH skeleton;The results of H₂-TPR,TEM and XPS show that Ni?NO3?2·6H₂O,ammonia and SiO₂ form nickel silicate after co-impregnation for 12 h and calcination at 800 ? for 2 h.Nickel silicate has a strong interaction with the silica supporter,good dispersion and excellent catalytic performance after the reduction;The higher concentration of ammonia and stronger alkaline environment has a positive effect on the dispersion of Ni particles.