Study On Steam Reforming Of Toluene Over Potassium Doped Ni-based Ordered Mesoporous Alumina Catalysts

Biomass undergoes biomass gasification technology to generate syngas.The tar generated in the process of generating syngas will reduce the efficiency of biomass gasification,and the presence of tar will block or corrode downstream pipelines.The existence of tar is one of the main problems faced by the industrialized biomass gasification technology,and efficient removal of tar is necessary.The composition of tar in gas production is complex,and the use of toluene as a model compound represents a stable aromatic ring structure.Among the existing tar removal methods,the steam reforming method in the catalytic method can further convert the tar into useful gas,thereby improving the overall gasification efficiency,and a suitable catalyst is the most important core of the catalytic method.Nickel-based catalysts are widely used in catalysis due to their high efficiency in removing tar,but they are prone to inactivation due to carbon deposits covering the surface of active nickel and sintering to cause particle agglomeration.In order to solve the problem of easy deactivation of nickel-based catalysts,ordered mesoporous aluminum was selected as the carrier to solve the sintering problem,and alkali metal potassium was added as an auxiliary agent to improve the catalyst activity.In this paper,the effects of potassium-added catalysts on toluene steam reforming and nickel-based ordered mesoporous alumina were studied,and the potassium-doped nickel-based ordered mesoporous alumina catalyst was used for toluene steam reforming.The special effect of adding alkali metal potassium on catalyst and reaction system,the principle of improving activity and stability.（1）Preparation and related characterization of catalysts with different potassium content x K-Ni-OMA and Ni/γ-Al₂O₃.Using a step-by-step solvent volatilization self-assembly method to prepare catalysts with different potassium content,the catalyst with ordered mesoporous structure can be obtained by adding appropriate amount of potassium,and the addition of potassium will cause the original amorphous Al₂O₃in the catalyst to change toγ-Al₂O₃phase transformation,excessive potassium will lead to the disappearance of the ordered mesoporous structure.The activity of the catalyst was evaluated by adding appropriate amount of potassium.The results showed that the conversion rate of catalyst to toluene steam reforming could be significantly improved,and the 2K-Ni-OMA catalyst with a potassium content of 2 wt%has high catalytic activity.The gas production analysis results further prove that the addition of an appropriate amount of potassium promotes the occurrence of water gas shift,and the presence of potassium enhances the catalyst’s ability to adsorb and activate water.Stability test results compare 2K-Ni-OMA,Ni-OMA and Ni/γ-Al₂O₃catalysts.The existence of ordered mesopores improves the stability of the catalysts,while the presence of alkali metals further improves the catalytic activity and stability.（2）In order to further prove the role of alkali metal potassium,we performed the following characterizations:H₂O-Pulse and H₂O-TPD.The two experimental results proved that as the potassium content increases,The doping of alkali metal potassium enhances the adsorption capacity of water on the catalyst surface.The effect of potassium addition on acid content was reflected in the results of FTIR and NH₃-TPD.The increase of potassium content the amount of acid of L acid decreases significantly,and the decrease of acid amount can effectively reduce the formation of gondoliers,This will reduce carbon deposits covering the surface and cause deactivation.The types of carbon deposits According to relevant characteristics,it is found that the addition of potassium makes carbon deposits more in the form of amorphous carbon.（3）The different spatial positions of potassium can further prove the role of potassium.The newly prepared 2K/Ni-OMA and Ni/2K-OMA have an ordered mesoporous structure,which is very close to the specific surface area and pore size distribution of2K-Ni-OMA.There is no obvious difference in activity evaluation and gas production analysis of the same catalyst.Appropriate addition of potassium improves the ability of the catalyst to adsorb and activate water and promote the occurrence of water gas shift reaction.（4）The big angle XRD results prove that the introduction of potassium into the EISA method in advance will cause the original amorphous alumina in the carrier to transform into the higher crystallinityγ-Al₂O₃phase.During the roasting process,the potassium salt easily reacts with water to KOH The form of solid Al₂O₃or Al（OH）₃reacts with KOH solution to form KAl（OH）₄,and KAl（OH）₄reacts with Al（OH）₃to form solid Al（OH）₃and KOH,which is finally calcined When the solid Al（OH）₃is decomposed intoγ-Al₂O₃phase and gaseous water.The above conditions lead to an increase in the crystallinity of the catalyst as the potassium content increases,which leads to the collapse of the pores and the disappearance of the ordered structure.Related characterization proved that more carbon exists in amorphous form on the three catalysts with the same potassium content,and the addition of potassium inhibits the graphitization process of carbon deposition.