Preparation And Properties Of Supported Non-noble Metal Catalysts By Atomic Layer Deposition

Catalytic technology plays a crucial role in the development of society.For most industrial processes,the preferred catalysts are heterogeneous?normally solid catalysts?.The traditional synthetic methods for heterogeneous catalysts,including impregnation,ion exchange and precipitation,provide limited control and lead to catalysts with mixtures of particle sizes and compositions,which leads to both wasted active material and potentially unwanted side reactions.Atomic layer deposition?ALD?has attracted wide attention owing to its characteristic self-limiting growth mechanism.Catalysts prepared by ALD have some potential benefits over traditional methods,including dispersed particle distribution,uniform composition,lower contamination from residual salts and the ability to penetrate highly porous supports.So far,ALD has been applied to heterogeneous catalysis in several different forms,such as synthesis of the active catalyst,modification of the catalyst support,introduction of promoters,improving stability,etc.Therefore,ALD has a broad prospect in the field of heterogeneous catalysis.Based on these backgrounds,there are still some drawbacks that restrict the further development of ALD in heterogeneous catalysis applications,such as the limitation of the kinds and amounts of the reported ALD precursors and the low growth rate of ALD process.In addition,owing to the high cost and limited resources of noble metal catalysts,the research on non-noble metal catalysts with excellent performance has become a challenge in the field of catalysis.Therefore,it is of particular significance to design corresponding ALD process to synthesize high-quality non-noble metal based nanomaterials and explore their application in heterogeneous catalysis.On the basic of these studies,in this paper,non-noble metal cerium-and copper-based nanomaterials were prepared by ALD and their applications in heterogeneous catalysis were explored.Detailed research contents are as follows:?1?Cerium amidinate complex?N-ⁱPr-AMD?₃Ce was synthesized,and the structure and thermal properties of complex were characterized by ¹H NMR,¹³C NMR,elemental analysis,melting point and thermogravimetry analysis?TGA?.The deposition experiments were carried out by ALD using the complex as the precursor and O₃ as the oxygen source.Moreover,the ALD process was optimized and the mechanism of film-forming process was also investigated.The results demonstrated that the synthesized complex possessed excellent volatility and sufficient thermal stability,which satisfied the requirements for ALD precursor.In addition,the film growth rate of corresponding ALD process reached 2.8?/cycle,and the deposited CeO_x films exhibited high purity and smooth surface.DFT results indicated that one typical ALD-CeO_x cycle may include the following process:?N-ⁱPr-AMD?₃Ce?ligand exchange on the SiO₂ surface?generating new surface||-A*or||-B*?ligand combustion with O₃ on the new surface?generating new Ce-OH groups for the next cycle.?2?On the basic of film deposition experiments,CeO_x/TiO₂ composite catalysts were prepared with the optimal ALD process,and the catalytic properties of the prepared catalysts was evaluated by photocatalytic degradation of organic pollutant phenol.Moreover,the morphology,composition and optical properties of the catalysts were studied through the corresponding characterization methods.The results demonstrated that the prepared ALD-CeO_x/TiO₂ photocatalysts possessed excellent catalytic activity and stability for degradation of phenol,which suggested the feasibility of the ALD-CeO_x process for the preparation of catalysts.The characterization results showed that CeO_x nanoparticles were uniformly deposited on the TiO₂ surface without changing the surface morphology and crystalline phase of Ti O₂,which was helpful in enhancing the absorption of light and promoting the separation and transfer of photogenerated electrons,therefore,improving the photocatalytic properties.?3?Copper amidinate complex?N-^sBu-AMD?₂Cu₂ was synthesized and characterized,and the feasibility of the combination of the complex and O₃ as the ALD-CuO precursors was evaluated through deposition experiments.Moreover,the ALD process was optimized by adjusting the pulse time and purge time of the precursors,deposition temperature and cycle number,and the surface morphology and composition of the films were studied.The results demonstrated that?N-^sBu-AMD?₂Cu₂ and O₃ were an efficient precursor combination for ALD process.A high film growth rate?2.5?/cycle?of corresponding ALD process was achieved,and the deposited CuO films exhibited high purity and smooth surface.?4?On the basic of film deposition experiments,CuO/TiO₂ composite catalysts were prepared with the optimal ALD process,and the catalytic properties of the prepared catalysts was evaluated by photocatalytic hydrogen production via water splitting.Moreover,the morphology,composition and optical properties of the catalysts were studied through the corresponding characterization methods.The results demonstrated that the prepared ALD-CuO/TiO₂ photocatalysts possessed excellent catalytic activity and stability for photocatalytic hydrogen production via water splitting,which suggested the feasibility of the ALD-CuO process for the preparation of catalysts.The characterization results showed that CuO subnanoparticles were successfully deposited on the surface of TiO₂ and exhibited uniform particle size and excellent dispersion.In addition,the ALD-CuO process hardly changed the surface morphology and crystalline phase of Ti O₂,and the ALD-CuO doping could favor the separation and transfer of photogenerated electrons and inhibite the recombination of electrons and holes,therefore,improving the photocatalytic properties.