Metal and metal oxide materials can be formed by various printing processes such as powder sintering, direct writing molding, and fused deposition. They have the advantages of low operating cost and high molding accuracy, and are a class of excellent 3D printing materials. At the same time, since the metal itself is a good monolithic catalyst skeleton material, the metal structure prepared by 3D printing can be loaded with the corresponding active components on the printing frame in a similar way to the traditional monolithic catalyst preparation. Commonly used metal and metal oxide direct printing processes include SLS and SLM. Such 3D printing equipment is generally expensive, but the technology is mature, the operation cost is low, and the printing accuracy is high, and the resulting material has high strength. Catalytically active components can be introduced into the printed structure by the method of loading to prepare different monolithic catalytic materials.
Ambrosi and others used 3D printed electrodes loaded with IrO2 materials to catalyze oxygen evolution (OER) reactions. Avril et al. Used 3D printing to prepare catalytic static mixers (CSMs) with different structures for continuous tube reactors to catalyze the hydrogenation of various organic molecules. Essa et al. Used the SLM process to design and prepare a monolithic catalyst bed with various structures, and evaluated its performance in the actual reaction process through calculations and experiments. In the above work, the raw materials used in the 3D printing molding process of integral materials are stainless steel, aluminum and other relatively mature materials. The active components only need to be dipped or coated on the surface of the skeleton. And metal oxide materials are not only simple in process, but also greatly reduce the cost of the preparation process. Another way of 3D printing of metal and metal oxide materials is to make a printing paste by adding a precursor powder or solution to a solvent and a viscosity modifier, and print by direct writing molding.
 The method can solve the problems of low specific surface area of ​​the supported metal monolithic catalyst, difficulty in combining active components and structural framework, and the like. This method is particularly suitable for various metal oxide materials such as alumina and zinc oxide. Taylor et al. Disperse the precursors of Fe and Ni uniformly in an organic system for the direct-write molding printing process. The obtained material is calcined to obtain a metal oxide structure skeleton, and after further reduction, a metal skeleton material can be obtained. Studies have shown that such materials have excellent mechanical properties, which provides a guarantee for the application of such materials in catalysis and adsorption. Tubio et al. Reported on the direct writing process with Cu (NO3) 2 and Al2O3 as precursors and cellulose-based materials as viscosity modifiers. After the material was calcined at 1400 ℃ to remove organic components, a Cu / Al2O3 catalyst with regular printing structure was obtained. The monolithic catalytic material has good printing accuracy (approximately 410 μm) and a large macro-porosity (57%), and its monolithic structure can obviously promote the Ullmann reaction catalytic activity of the material. The results show that in the absence of ligands, the yield of the target product can reach 78% ~ 94%, and the reaction time can be shortened to 2 ~ 4h. The team of Fan Tongxiang of Shanghai Jiaotong University prepared a photocatalytic material based on TiO2 with a multi-level pore structure through a direct writing molding process, and prepared a photocatalytic material with a leaf-like structure for the CO2 conversion process using the bionics principle. This process uses ethanol / water system as solvent, diisopropyl di (acetylacetonyl) titanate (TIA) as Ti precursor, dodecylbenzenesulfonic acid as pore-forming agent, and sol system formed by TIA hydrolysis process To ensure the rheological requirements of the printing process. The TiO2 photocatalytic material obtained by this process has a good multi-stage pore structure and a large specific surface area (237-267m2 / g), and at the same time, the template method can be used to control the microscopic pore size more effectively. The photocatalytic CO2 reduction process of this material can achieve CO1 and CH4 output of 0.21μmol / (g · h) and 0.29μmol / (g · h), respectively, which is significantly higher than the yield of conventional photocatalyst [0.11μmol / (g · h ) And 0.05 μmol / (g · h)].