Rational Design And Preparation Of Hierarchical Monoliths Through 3D Printing For Syngas Methanation

Hierarchical monoliths have been widely used in adsorption,catalysis,electrode and capacitor due to the excellent heat and mass transfer performance and accessible surface area.The conventional monolithic material have often been modified by thermal treating,coating or in situ growing zeolite precursor and carbon nanofiber.Transport pore configurations in monolithic catalysts further modulate the adsorption and catalytic performance of the material by affecting the mass and heat transfer during the chemical reaction process,which have scarcely been studied.Therefore,rational design and synthesis of microchannel are essential to further simulate and optimize monolith materials.3D printing technology has the unique advantages in 3D additive manufacturing.The key advantage of 3D printing is to design tortuous channels modulating transport performances in hierarchical monolith rather than simple straight compared with conventional extrusion molding.In this study,3D microchannel monolithic catalysts were designed by Solidworks and prepared by self-sacrificial 3D template method.Comparison with the hydraulic materials(cement,ceramics),Al2O3,SiO2,and phenolic resin materials for shaping revealed that the phenolic resin and cement materials had the better ability to form monolith.However,cement monolith has lower specific surface and is easy to collapse under high temperature conditions.Therefore,phenolic resin materials was employed in the study.To explore the effect of microchannel structural characteristics on catalyst performance,for the first time,cylinder,and tetrahedron and tetrakaidecahedron periodic structure were set up by 3D printing and successfully as the hard template to prepare phenol-formaldehyde based hierarchical monolith for methanation.Syngas methanation which is a high exothermic reaction was evaluated over these monolith.Results show that the size,type,bifurcation angle and porosity of channel structure can precisely be modulated by 3D printing.SEM presents that macropore and mesopore are connected throughout.More importantly,through modulating the tortuosity of macropores,Ni-Al2O3/C monolith with 1.25 mm diameter,109.5°furcation angle,30%porosity tetrahedral channel,shows excellent 74.1%CH4 yield as well as prominently decreasing in temperature gradient and pressure drop at T=3750C,p=0.1 MPa,GHSV=24000 h-1 reaction conditions compared with other conventional catalysts,The pressure drop sharply reduced from 6.0 kPa of the powder to 0.4 kPa,and the temperature rise of the unit CO conversion is reduced from?T1%=1.82? of the powder to ?T1%=0.89?.High mass and heat transport cooperating with reaction activity efficiently facilitate the improvement of catalytic performance.The successful synthesis of such fascinating materials paves the way to explore the application of hierarchical monolith in separation and reaction processes especially for industrial catalysts design.