Method for catalyzing formic acid dehydrogenation by using PdAu nanosheet catalyst under visible light
阅读说明：本技术 用PdAu纳米片催化剂可见光催化甲酸脱氢的方法 (Method for catalyzing formic acid dehydrogenation by using PdAu nanosheet catalyst under visible light ) 是由 万超 周柳 王嘉佩 吴胜华 许立信 张代林 于 2019-09-18 设计创作，主要内容包括：本发明公开了一种用PdAu纳米片催化剂可见光催化甲酸脱氢的方法,属于化学化工技术领域。本发明将制备好的PdAu纳米片催化剂置于夹套反应器中,通过恒温循环槽控制反应在一定温度进行,将可见光从夹套反应器上方照射反应液,接着将甲酸和甲酸钠混合液加入反应器中进行反应,生成的氢气采用排水法收集。与传统的负载型催化剂不同的是：根据本发明,调节催化剂中金属钯、金的含量及Mxene-TiO<Sub>2</Sub>含量就可以制得用于光催化甲酸脱氢制氢气的高活性、高选择性负载型PdAu纳米片催化剂。使用该催化剂进行可见光甲酸脱氢反应,脱氢转化率和选择性均为100％,反应的TOF值大于850h<Sup>-1</Sup>,循环使用8h,反应的TOF值仍大于834h<Sup>-1</Sup>。(The invention discloses a method for catalyzing formic acid dehydrogenation by using a PdAu nanosheet catalyst through visible light, and belongs to the technical field of chemical engineering. The method comprises the steps of placing a prepared PdAu nanosheet catalyst in a jacket reactor, controlling the reaction to be carried out at a certain temperature through a constant-temperature circulating tank, irradiating reaction liquid by visible light from the upper part of the jacket reactor, adding mixed liquid of formic acid and sodium formate into the reactor for reaction, and collecting generated hydrogen by adopting a drainage method. Unlike conventional supported catalysts: according to the invention, the contents of metal palladium and gold and Mxene-TiO in the catalyst are adjusted 2 The supported PdAu nanosheet catalyst with high activity and high selectivity for preparing hydrogen by photocatalytic formic acid dehydrogenation can be prepared. The catalyst is used for visible light formic acid dehydrogenation reaction, and the dehydrogenation conversion rate and selectivity are bothThe TOF value of the reaction is more than 850h and is 100 percent ‑1 The reaction time is 8h after recycling, and the TOF value of the reaction is still larger than 834h ‑1 。)
1. A method for catalyzing formic acid dehydrogenation by using a PdAu nanosheet catalyst under visible light is characterized by comprising the following steps: placing a PdAu nanosheet catalyst in a jacket reactor, controlling the reaction at 10-40 ℃ through a constant-temperature circulating tank, irradiating the reaction solution from the upper part of the jacket reactor by visible light with the wavelength of lambda being more than 400nm, and then, mixing the reaction solution with the solvent with the molar ratio of 1: (0.2-0.6) adding the mixed solution of formic acid and sodium formate into a reactor for reaction to obtain a product hydrogen;
The mass ratio of the catalyst to the mixed solution of formic acid and sodium formate is 1 (30-50);
The PdAu nanosheet catalyst comprises Pd, Au and Mxene-TiO2And g-C3N4Nanosheets wherein Pd is derived from palladium chloride and Au is derived from chloroauric acid, Mxene-TiO2Derived from Mxene-Ti2AlC，g-C3N4The nano-sheet is prepared by roasting melamine and lithium chloride;
the PdAu nanosheet catalyst is prepared by the following steps:
(1) calcining melamine and lithium chloride in certain ratio under certain calcining condition and atmosphere, washing at certain temperature for certain period, and filtering to obtain g-C3N4Nanosheets;
The mass ratio of the melamine to the lithium chloride is 1: (4-8); the roasting temperature is 520-550 ℃, the roasting time is 4-7 hours, the atmosphere is nitrogen, the water washing temperature is 20-45 ℃, and the water washing time is 40-50 hours;
(2) Taking a certain amount of Ti2Adding AlC into hydrofluoric acid solution with certain concentration for a period of time, and freeze-drying to obtain Ti2C；
The mass concentration of the HF is 30-50 wt%, and the treatment time is 4.0-6.0 h;
(3) Mixing Ti2C and g-C3N4Placing the nano-sheets in a hydrothermal synthesis kettle containing 40ml of deionized water according to a certain molar ratio, and adding NaHSO with a certain concentration3ultrasonically dispersing the solution for a period of time, putting the solution at a certain temperature for hydrothermal synthesis for a period of time, filtering, washing with water, and freeze-drying to obtain the Mxene-TiO2@g-C3N4A nanosheet carrier;
the Ti2C and g-C3N4The molar ratio of the nano-sheets is 1: (20 to 35) NaHSO3The concentration is 0.03-0.05 mol/L, the hydrothermal synthesis temperature is 120-150 ℃, and the hydrothermal synthesis time is 8-12 h;
(4) Freeze drying the obtained porous Mxene-TiO2@g-C3N4Placing the nanosheet carrier in a palladium chloride and chloroauric acid solution with a certain composition, reducing for a period of time at a certain temperature by using a formaldehyde solution, and centrifugally drying to obtain PdAu/Mxene-TiO2@g-C3N4A nanosheet catalyst;
The palladium chloride, the chloroauric acid and the Mxene-TiO2@g-C3N4The molar ratio of the nano-sheets is 1: (0.1-0.3): (20-25), the concentration of formaldehyde is 0.05-0.09 mol/L, the reduction temperature is 10-25 ℃, and the reduction time is 5-8 h.
2. The method of visible-light catalyzed formic acid dehydrogenation with PdAu nanosheet catalyst of claim 1, wherein:
The mass ratio of the melamine to the lithium chloride is 1: 8; the roasting temperature is 550 ℃, the roasting time is 4 hours, the atmosphere is nitrogen, the washing temperature is 20 ℃, and the washing time is 50 hours;
The mass concentration of the HF is 50 wt%, and the treatment time is 4.0 h;
The Ti2C and g-C3N4The molar ratio of the nano-sheets is 1: 35, NaHSO3the concentration is 0.05mol/L, the hydrothermal synthesis temperature is 150 ℃, and the hydrothermal synthesis time is 8 h;
The palladium chloride, the chloroauric acid and the Mxene-TiO2@g-C3N4The molar ratio of the nano-sheets is 1: 0.3: 25, the concentration of formaldehyde is 0.09mol/L, the reduction temperature is 10 ℃, and the reduction time is 5 hours;
The mass ratio of the catalyst to the mixed solution of formic acid and sodium formate is 1:50, and the reaction temperature is 40 ℃; the molar ratio of the formic acid to the sodium formate is 1: 0.6.
Technical Field
The present invention belongs to the field of chemical technologyThe field of operation, in particular to the use of PdAu/TiO2@g-C3N4A method for dehydrogenating formic acid by visible light catalysis of a nanosheet catalyst.
Background
Hydrogen is an efficient, clean and green energy source, but hydrogen has very low volumetric and mass energy densities, and efficient and safe storage and transportation of hydrogen becomes a major challenge for hydrogen energy utilization. To solve this problem, researchers have developed and explored a variety of different types of hydrogen storage materials, of which formic acid has received much attention from researchers due to its advantages, such as non-toxicity, high mass energy density, and safe storage and transportation.
The key point of the application of the current formic acid as a hydrogen storage material lies in the development of a high-efficiency dehydrogenation catalyst, and the catalysts researched by researchers at present mainly focus on two types, namely a homogeneous catalyst and a fern catalyst. Wherein the homogeneous catalyst is mainly a metal complex of ruthenium, rhodium, iridium, iron and cobalt. Lican et al (CN105772090B) reported a class of computational dehydrogenation catalysts that can be used in aqueous systems, the catalysts include metals and ligands, the metals are iridium, rhodium, ruthenium, iron, copper, cobalt, palladium, platinum, etc., the ligands are heterocyclic compounds containing C ═ N double bonds in the structure; under the alkali-free condition, the maximum TOF at 90 ℃ can reach 37.5 x 104h-1. Although homogeneous catalysts exhibit excellent catalytic performance, their difficult separation for recycling greatly limits their scale-up applications. Liu and the like are designed with AuxPdyCNS catalyst and its application in visible light catalytic dehydrogenation of formic acid with TOF value as high as 1017.8h-1(Applied Catalysis B: Environmental 252(2019) 24-32). Therefore, the research on heterogeneous catalysts, especially heterogeneous catalysts for high efficiency dehydrogenation of formic acid under the action of visible light, is one of the hot spots in the current research.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a new method for preparing PdAu/Mxene-TiO by using PdAu/Mxene2@g-C3N4A method for dehydrogenating formic acid by visible light catalysis of a nanosheet catalyst, namely PdAu/Mxene-TiO2@g-C3N4Nanosheet catalyst inUnder the action of visible light, the formic acid can be completely dehydrogenated under a relatively mild condition, and the catalyst has good catalytic activity, selectivity and stability.
The technical scheme adopted by the invention for solving the technical problem is as follows.
The method for catalyzing formic acid dehydrogenation by using the PdAu nanosheet catalyst through visible light comprises the steps of placing the PdAu nanosheet catalyst in a jacket reactor, controlling the reaction to be carried out at 10-40 ℃ through a constant-temperature circulating groove, irradiating reaction liquid from the upper part of the jacket reactor by using visible light with the wavelength lambda being more than 400nm, and then, mixing the reaction liquid in a molar ratio of 1: (0.2-0.6) adding the mixed solution of formic acid and sodium formate into the reactor for reaction to obtain the product hydrogen.
The mass ratio of the catalyst to the mixed solution of formic acid and sodium formate is 1 (30-50).
The PdAu nanosheet catalyst comprises Pd, Au and Mxene-TiO2And g-C3N4Nanosheets wherein Pd is derived from palladium chloride and Au is derived from chloroauric acid, Mxene-TiO2Derived from Mxene-Ti2AlC，g-C3N4The nano-sheet is prepared by roasting melamine and lithium chloride.
The PdAu nanosheet catalyst is prepared by the following steps:
(1) Calcining melamine and lithium chloride in certain ratio under certain calcining condition and atmosphere, washing at certain temperature for certain period, and filtering to obtain g-C3N4Nanosheets;
the mass ratio of the melamine to the lithium chloride is 1: (4-8); the roasting temperature is 520-550 ℃, the roasting time is 4-7 hours, the atmosphere is nitrogen, the water washing temperature is 20-45 ℃, and the water washing time is 40-50 hours;
(2) Taking a certain amount of Ti2Adding AlC into hydrofluoric acid solution with certain concentration for a period of time, and freeze-drying to obtain Ti2C；
The mass concentration of the HF is 30-50 wt%, and the treatment time is 4.0-6.0 h;
(3) Mixing Ti2C and g-C3N4the nano-sheets are placed in 40ml of deionized water according to a certain molar ratioHydrothermal synthesis kettle, adding NaHSO with certain concentration3Ultrasonically dispersing the solution for a period of time, putting the solution at a certain temperature for hydrothermal synthesis for a period of time, filtering, washing with water, and freeze-drying to obtain the Mxene-TiO2@g-C3N4a nanosheet carrier;
The Ti2C and g-C3N4The molar ratio of the nano-sheets is 1: (20 to 35) NaHSO3The concentration is 0.03-0.05 mol/L, the hydrothermal synthesis temperature is 120-150 ℃, and the hydrothermal synthesis time is 8-12 h;
(4) freeze drying the obtained porous Mxene-TiO2@g-C3N4Placing the nanosheet carrier in a palladium chloride and chloroauric acid solution with a certain composition, reducing for a period of time at a certain temperature by using a formaldehyde solution, and centrifugally drying to obtain PdAu/Mxene-TiO2@g-C3N4a nanosheet catalyst;
The palladium chloride, the chloroauric acid and the Mxene-TiO2@g-C3N4the molar ratio of the nano-sheets is 1: (0.1-0.3): (20-25), the concentration of formaldehyde is 0.05-0.09 mol/L, the reduction temperature is 10-25 ℃, and the reduction time is 5-8 h.
Further, the mass ratio of melamine to lithium chloride is 1: 8; the roasting temperature is 550 ℃, the roasting time is 4 hours, the atmosphere is nitrogen, the washing temperature is 20 ℃, and the washing time is 50 hours; the mass concentration of the HF is 50 wt%, and the treatment time is 4.0 h; the Ti2c and g-C3N4The molar ratio of the nano-sheets is 1: 35, NaHSO3the concentration is 0.05mol/L, the hydrothermal synthesis temperature is 150 ℃, and the hydrothermal synthesis time is 8 h; the palladium chloride, the chloroauric acid and the Mxene-TiO2@g-C3N4The molar ratio of the nano-sheets is 1: 0.3: 25, the concentration of formaldehyde is 0.09mol/L, the reduction temperature is 10 ℃, and the reduction time is 5 hours; the mass ratio of the catalyst to the mixed solution of formic acid and sodium formate is 1:50, and the reaction temperature is 40 ℃; the molar ratio of the formic acid to the sodium formate is 1:0.6, at this point, the hydrogen selectivity was 100%, the formic acid conversion was 100%, and the TOF value of the reaction was 1360h-1。
Compared with the prior art, the invention has the beneficial effects that:
1. The invention relates to Mxene-Ti2Synthesis of oxygen-deficient Mxene-TiO by using AlC as precursor2And then hydrothermally synthesizing high-dispersity Mxene-TiO2@g-C3N4Nanosheet support material, Mxene-TiO2@g-C3N4The nano-sheet carrier material has good electron transfer performance and photoinduction performance, and further adopts a dipping reduction method PdAu/Mxene-TiO2@g-C3N4the nano-sheet catalyst is a supported PdAu alloy synthesized by formaldehyde reduction under mild conditions, and the reducing agent can realize the regulation and control of a PdAu alloy structure and uniform loading on a carrier. The charge distribution of the metal valence band orbit is changed by adjusting the proportion of metal components, the concentration of a reducing agent and reaction conditions, and the stability of catalytic reaction is further adjusted. In addition, the influence of multi-component Metal composition and multi-functional groups on the surface of the carrier obviously enhances the Strong interaction (SMSI) of the Metal and the carrier between the Metal and the carrier, and effectively improves the catalytic activity.
2. The invention adopts a dipping reduction method, firstly adopts a salt melting method to synthesize g-C3N4Nanosheets, treating Ti with hydrofluoric acid2Ti from AlC (Mxene)2C, mixing g-C3N4Nanosheet and Ti2C, preparing Mxene-TiO by hydrothermal treatment2@g-C3N4Nanosheet, Mxene-TiO to be obtained2@g-C3N4Placing the nanosheets in a palladium chloride and chloroauric acid solution with a certain composition, reducing for a period of time at a certain temperature by using a formaldehyde solution, and centrifugally drying to obtain PdAu/Mxene-TiO2@g-C3N4The nanosheet catalyst has high activity and selectivity under the action of visible light. The catalyst is used for visible light catalytic formic acid dehydrogenation reaction, the dehydrogenation conversion rate and selectivity are both 100%, and the TOF value of the reaction is more than 850h-1the reaction time is 8h after recycling, and the TOF value of the reaction is still larger than 834h-1。
Detailed description of the invention
The present invention will be described in further detail by way of examples. The examples are not to be construed as limiting the invention.
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