Study On The Preparation Of LaNiO₃ Perovskite Catalysts And Performance For POM Reaction

Although the explored reserves of coalbed methane resource are very plentiful in our country,ranking third in the word,the utilization of it is very low.Most of the low concentration of coalbed methane are directly emptied which not only caused the waste of resources,but also exacerbated the greenhouse effect.Partial oxidation of methane?POM?reaction is one of the effective ways to utilize low concentration coalbed methane.It possesses appropriate products ratio value?H₂/CO=2?which is beneficial for generating a series of chemical products.Additionally,it has merit of low energy consumption,high space velocity,small reactor,rapid reaction rate and so on.Ni-based catalysts which have the most promise to realize the industrialzation had attracted enormous attritions due to outstanding catalytic performance and low price.However,the Ni based catalysts are easier to inactivate by reason of sintering and coke deposition under the high temperature condition.In order to solve aforementioned questions and improve the lifetimes and performances of catalysts,we prepared order mesoporous structure La NiO₃ perovskite catalysts,three-dimensional ordermacroporous of inverse opal structure LaNiO₃ catalysts,mesoporous LaNiO₃ catalysts with three dimensional order macroporous SiO₂ as skeleton,conventional LaNiO₃ catalysts and used the XRD?BET?SEM?TEM?TPR?TGA analysis methods to measured their physicochemical properties.Investigating the size of particles,specific surface area,dispersion of active ingredients,porous structure and reaction condition?temperature,space velocity,lifetime?and other factors impacted on the catalytic performance,anti-sintering and anti coke deposition.The main contents are as follows:1.order mesoporous LaNiO₃ perovskite catalystsOrder mesoporous LaNiO₃ catalysts?m-LN?was prepared using the SBA-15 as hard template according to the modified nanocasting method.Compared to the conventional LaNiO₃ catalyst?b-LN?prepared by citrate method,the results are as follow:?1?the modified nanocasting method with aid of ultraphonic,vacumm and centrifugation could deliver more precursors into the channels and reduce residual at external surface of template.The narrow porous channels of SBA-15 had a function on controlling the size of particles which m-LN catalysts with a particle size of 5.9-6.7 nm are smaller than b-LN?50-200 nm?.After removing template,the formation of mesoporous structure greatly improved the surface area.?2?The Ni particle size of reduced m-LN catalysts were 9.3 nm and were almost no change after reaction.The Ni particles sizes of b-LNR were 17.9 nm and had a prominent increase after reaction.The TPR analysis of m-LN catalysts showed lower reduction temperature and largeramounts of H2 consumption.?3?The catalytic activity of all the samples in the POM reaction improved with the increase of temperature and had a slight decrease with the increase of space velocity.Under the same reaction conditions,m-LN catalyst showed excellent catalytic performance and anti-carbon property compared to b-LN.The CH4 conversion of m-LN catalyst achieved 96% at 800? than b-LN?82%?.This result was attributed to the enhanced specific surface area,high metal dispersion,and smaller Ni particle size and ordered mesoporous structure.2.Three-dimensional order macroporous LaNiO₃ catalystsThree-dimensional ordered macroporous LaNi O3 catalysts were prepared by using 300 nm PMMA colloidal crystal template.Compared with the conventional LaNiO₃ catalyst?b-LN?,the results showed:?1?the diameter of PMMA microspheres increased with the addition of monomer MMA and initiator K2S2O8,decreased with the raise of the reaction temperature and the flow rate of N2.?2?The quality of colloidal crystal obtained by centrifugal deposition method is more excellent than natural sedimentation method.3000 r/min centrifugal speed can obtain the most flat and order template for 300 nm PMMA microspheres.?3?The LaNiO₃ precursor solution was added to the void of the prepared colloidal crystal template and then can obtain inverse opal structure LaNiO₃ perovskite catalysts with pore size of 140 nm after removing the template.The POM reaction test showed that the catalytic performance of 3-DOM catalyst is higher than the b-LN catalyst.However,the POM tests for3-DOM catalysts did't achieve the anticipative result.It may be related to the catalysts pore size.3.Mesoporous LaNiO₃ catalysts with 3DOM SiO₂ as skeleton Mesoporous LaNiO₃ catalysts?P-LN?with a 3DOM SiO₂ skeleton were prepared via filling the LaNiO₃ perovskite material in three dimensional ordered macroporous SiO₂ voids.The experimental results showed that:?1?P-LN catalysts possess smaller particles size?large surface area and mesoporous structure.Additionally,catalysts particles distribution was more hemogeneous and almost no agglomeration and sintering of the phenomenon.?2?Compared with b-LN catalyst under the same reaction conditions,the catalytic activity of P-LN was higher and the CH4 conversion achieved 95% at 800?.Additionally,the former anti coke deposition performance was stronger than the latter.?3?Comparing the catalytic performance of the P-LN catalysts with the 3-DOM LN catalysts,we can observe that the catalytic performance of the P-LN catalysts were better than the latter under the same reaction conditions.At 800 ?,the conversion of P-LN catalysts achieved 95% which was higher than 3-DOM LN catalyst?87%?.It means that the modified P-LN catalysts can play a role in improving the catalytic performance.