Design And Preparation Of Monolithic Catalysts For Semi-Hydrogenation Of Acetylene

Hydrogenation catalysis has a wide range of applications in the chemical industry,in which the removal of trace acetylene impurities（0.5-2.0%）from ethylene feedstock produced by steam cracking plays a crucial role in the subsequent industrial production of high-quality polyethylene.The process of semi-hydrogenation requires the catalyst not only to achieve the highly active hydrogenation of acetylene to ethylene,but also to avoid the excessive hydrogenation of ethylene to ethane due to the poisoning effect of acetylene on the ethylene polymerization catalysts and the terminating effect of ethane on the ethylene polymerization process.The fixed bed reactor for semi-hydrogenation of acetylene is usually loaded with granular catalyst and inert filler mixtures,in which packed particles could give rise to a non-homogeneous access to the catalytic surface and an uneven temperature distribution,further resulting in the occurrence of side reactions.3D printing technology can achieve precise regulation of complex structures in monolithic catalysts to effectively enhance the mass/heat transfer process in the reaction.However,inorganic catalytic materials possess the poor processability that will easily collapse,which limit their application as the skeleton of monolithic catalysts.Therefore,the design and preparation of monolithic catalysts with high throughput and high separation of the syngas,reducing energy consumption,and significantly improving catalytic efficiency is of great significance in the semi-hydrogenation of acetylene.This study takes semi-hydrogenation of acetylene as the target reaction,a series of oxometallate intercalated layered double hydroxides（LDH）precursors were prepared by tuning cations of the brucite-like layers and interlayer anions to endow the corresponding calcined products with the mechanical property,the high adsorption capacity,tunable basicity of the surface,highly and stably dispersed supported active sites,further achieving the construction of high-performance 3D printing monolithic catalysts for the semi hydrogenation of acetylene.The specific works are as follows:（1）The intercalation of aluminate modified the molar ratio of divalent and trivalent metals(Mg²⁺/Al³⁺=0.5)in the as prepared aluminate-intercalated layered double hydroxide（AI-LDH）precursors.The synchronism of dehydration of laminates and intercalated ions is beneficial for the conversion of LDH to stiff spinel-type metal oxides at a low temperature with high specific surface areas.Ni/Mg Al₂O₄ catalyst was further prepared by the same strategy except for introducing Ni²⁺during coprecipitation process,and the net trap effect of LDH laminates could effectively separate Ni to avoid sintering during the calcination process.The Ni/Mg Al₂O₄ catalyst has a high-specific-surface-areas（309 m²/g）,significant Ni size effect and enhanced metal-support interaction,which showed high catalytic activity（>99%）,selectivity towards ethylene（>80%）,and excellent long-term stability（28 hrs）.（2）Hierarchical spinel monolithic catalysts with a porous woodpile architecture were fabricated via extrusion-based 3D printing of the inks based on AI-LDH precursors followed by low temperature calcination.Due to the improvement of the mechanical properties of the overall structure by the intercalated aluminate and the generation of the corresponding spinel crystal phase,the printed patterns remain extremely stable during the calcination process.Spinel-type metal oxides catalysts with woodpile architecture,mesoporous,and uniformly dispersed noble metals（Pd,Pt,and Rh）were manufactured by the 3D printing strategy.The 3D-printed Pd loaded spinel-type Mg Al-mixed metal oxide（3D-AI-Pd/MMO）catalyst with hierarchical porous structures could effectively enhance mass/heat transfer during the reaction process,exhibited 100%conversion with more than 84%ethylene selectivity at60 ^oC in semi-hydrogenation of acetylene and excellent stability（100 hrs）.（3）By the similar synthesis strategies mentioned above,Ni Al LDHs with different interlayer oxometallate anions（OM-LDH）have been further prepared.Moreover,a series of 3D porous woodpile like Ni supported mixed metal oxide（Ni/MMO）catalysts doped with different elements（Mo,V,and W）were realized by direct ink writing（DIW）technology.The intercalated molybdate,vanadate and tungstate had the supporting effect which were analogous to the interlayer aluminate galleries of the AI-LDH,endowing the monolithic catalyst with excellent mechanical properties.In addition,doping the Mo,V,and W into Ni/MMO could effectively promote the dispersion of Ni sites in the catalyst.3D printing Ni/MMO catalyst(3D-Mo O₄^2--Ni/MMO)derived from molybdate intercalated Ni Al LDHs with highly dispersed Ni and enhanced metal-support effect displayed highly activity（>99%）,chemo-selective to ethylene（>85%）,and satisfactory long-term stability during a 60 hrs test.