Catalyst for selectively catalyzing hydrogenation of aromatic aldehyde ketone compounds as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for selectively catalyzing hydrogenation of aromatic aldehyde ketone compounds, the catalyst is TiO2 (B)-loaded atomic-scale dispersed Pd atoms, TiO2 (B) is of an ultrathin two-dimensional structure, and the loading amount of Pd is 0.1-1.5 wt%. And high reaction activity and high selectivity are realized by using the ultrathin two-dimensional structure of the load TiO2 (B) and the Pd atoms dispersed in an atomic scale.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a catalyst for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, and a preparation method and application thereof. Background Art

[0002] Aromatic alcohols are an important class of chemical intermediates. They are raw materials for synthetic drugs and spices. They are also the main components of some aromatic rose oils. They have an aromatic smell and are often used as fragrances for cosmetics. At present, the industry mainly uses the reduction of aromatic ketones or aromatic aldehydes to prepare aromatic alcohols. Stoichiometric reducing agents include sodium borohydride and lithium aluminum tetrahydride, etc. This method is relatively costly and produces a lot of waste. On the other hand, aromatic alcohols are obtained by catalytic hydrogenation of the corresponding aromatic ketones or aromatic aldehydes, where precious metal catalysts include Pd, Pt, Ru and Rh-based catalysts. Such catalysts have high catalytic activity and stability, but there are problems with selectivity, that is, aromatic alcohols are easily further hydrogenated and deoxygenated to produce alkanes. It is well known that selectivity is crucial for chemical transformations, especially when a chemical reaction involves multiple reactive groups in multiple continuous reactions and needs to stay in the intermediate product. One important example is the selective catalytic hydrogenation of aromatic aldehydes and ketones to prepare the corresponding aromatic alcohols. In this reaction, both the catalytic hydrogenation of carbonyl groups to alcohols and the hydrogenation and dehydration of alcohols are possible, which makes it difficult to prohibit the hydrogenation and dehydration of alcohols under the hydrogenation conditions that ensure the rapid conversion of carbonyl groups to alcohols. Therefore, it is still challenging to construct a catalytic system that achieves both high conversion and high selectivity. In addition, based on the price of precious metals, improving the atomic utilization of precious metals is a good strategy to reduce costs. Atomically dispersed catalysts can achieve 100% utilization of metals, while minimizing costs, and have the most uniform active sites, that is, they can achieve both high activity and high selectivity at the same time. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides atomically dispersed Pd atoms as catalysts, utilizing the ultra-thin two-dimensional structure of the supported material TiO2(B) and atomically dispersed Pd atoms to achieve high reaction activity and high selectivity.

[0004] Specifically, on the one hand, the present invention provides a catalyst for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, characterized in that the catalyst is atomically dispersed Pd atoms supported on TiO2(B), TiO2(B) is an ultra-thin two-dimensional structure, and the Pd loading amount is 0.1wt% to 1.5wt%.

[0005] In some embodiments, the loading amount of Pd is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt% or 1.5 wt%.

[0006] In some embodiments, the loading amount of Pd is 0.5 wt % to 1.5 wt %.

[0007] On the other hand, the present invention also provides a method for preparing a catalyst for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, characterized in that it comprises the steps of:

[0008] (1) Preparation of TiO2(B) nanosheets: TiCl4 was added to ethylene glycol, and the resulting clear and transparent liquid was heated at 120°C for 4 hours, cooled, washed with ethylene glycol by centrifugation, and dried to obtain TiO2(B) nanosheets; wherein the volume ratio of ethylene glycol to TiCl4 was 30:1;

[0009] (2) Ultrasonic dispersion of the TiO2(B) nanosheets obtained above in water, adding H2PdCl4 aqueous solution under stirring, ultrasonic dispersion, ultraviolet irradiation under stirring for 1 hour, centrifugation, water washing, and vacuum drying to obtain a two-dimensional Pd1 / TiO2 catalyst; wherein the mass ratio of TiO2(B) nanosheets to Pd in ​​H2PdCl4 is (1000-65):1. Preferably, the mass ratio of TiO2(B) nanosheets to Pd in ​​H2PdCl4 is (200-65):1.

[0010] On the other hand, the present invention also provides use of the catalyst or the catalyst prepared by the preparation method in selectively catalyzing the hydrogenation of aromatic aldehydes and ketones to obtain aromatic alcohols.

[0011] On the other hand, the present invention also provides a method for selective catalytic hydrogenation of aromatic aldehydes and ketones, characterized in that it includes dispersing a two-dimensional Pd1 / TiO2 catalyst in a solvent, adding aromatic aldehydes and ketones to react at a certain temperature and a certain H2 pressure to obtain aromatic alcohols as hydrogenation products of aromatic aldehydes and ketones; the two-dimensional Pd1 / TiO2 catalyst is the catalyst described in the present invention or the catalyst prepared by the preparation method.

[0012] In some embodiments, the reaction solvent is selected from one or more of water, alcohol, and tetrahydrofuran; preferably, the reaction solvent is selected from one or more of water, methanol, ethanol, isopropanol, tert-butanol, and tetrahydrofuran.

[0013] In some embodiments, the aromatic aldehyde and ketone compound is selected from one or more of substituted or unsubstituted aromatic aldehydes and substituted or unsubstituted aromatic ketones.

[0014] In some embodiments, the aromatic aldehyde ketone compound has a structure as described in formula (I);

[0015]

[0016] Among them, R 1 is selected from: H and substituted or unsubstituted alkyl;

[0017] R 2 is selected from H, halogen, hydroxyl, mercapto, cyano, amino, nitro, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkylamino, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkenyl and substituted or unsubstituted alkynyl; optionally, two adjacent R 2 , together with the atoms to which they are attached, form a substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl or substituted or unsubstituted heterocyclyl;

[0018] X 1 , X 2 , X 3 , X 4 and X 5 are independently CH or N; X 1 , X 2 , X 3 , X 4 and X 5 Not all are N;

[0019] n is selected from 0, 1, 2, 3, 4 or 5.

[0020] In some embodiments, the aromatic aldehyde and ketone compound has a structure as described in formula (II);

[0021]

[0022] R 1 is H or alkyl; preferably, the alkyl is selected from: methyl, ethyl or propyl;

[0023] R 2 is H, hydroxyl, halogen, alkyl or alkoxy; preferably, the alkyl is selected from: methyl, ethyl or propyl; the alkoxy is selected from: methoxy or ethoxy.

[0024] In some embodiments, the reaction temperature is selected based on the freezing point and boiling point of the solvent used; the reaction pressure is based on the tolerable pressure of the reactor used.

[0025] In some embodiments, the molar ratio of Pd to aromatic aldehyde and ketone compounds in the two-dimensional Pd1 / TiO2 catalyst may be 1:(10-10000); preferably 1:2000.

[0026] Beneficial Effects

[0027] Compared with existing technologies:

[0028] (1) The high activity of the present invention comes from the H+ and H- generated by heterolytic activation, which is beneficial to the hydrogenation of polar unsaturated bonds (C=O), so no activation site is required. In contrast, the prior art uses hydrogen atoms (·H) generated by homolytic activation, which is not beneficial to the hydrogenation of polar unsaturated bonds (C=O), so an activation site is required.

[0029] (2) The high selectivity of the present invention is due to the absence of the Pd metal surface, which results in the CO bond of the product alcohol not being able to lie flat and adsorb on the metal surface to undergo hydrogenation bond cleavage, thereby achieving high catalytic selectivity.

[0030] Terminology

[0031] Certain embodiments of the present invention are now described in detail. The present invention is intended to cover all substitutions, modifications and equivalent technical solutions, which are all included in the scope of the present invention as defined in the claims. It should be appreciated by those skilled in the art that many methods and materials similar or equivalent to those described herein can be used to practice the present invention. The present invention is by no means limited to the methods and materials described herein. In the event that one or more of the combined documents, patents and similar materials are different from or contradictory to the present application (including but not limited to defined terms, term applications, described technologies, etc.), the present application shall prevail.

[0032] It should be further appreciated that certain features of the invention, which for clarity are described in multiple separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which for brevity are described in a single embodiment, may also be provided separately or in any suitable sub-combination.

[0033] Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. All patents and publications related to the present invention are incorporated herein by reference in their entirety.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0035] In the following, all numbers disclosed herein are approximate, regardless of whether the word "about" or "approximately" is used. The value of each number may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15% or 20%. Whenever a number with a value of N is disclosed, any number with a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15% or N+ / -20% will be explicitly disclosed, where "+ / -" means plus or minus.

[0036] The term "wt%" means percent by mass.

[0037] The terms "optional", "optionally" or "arbitrarily", "optionally" mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not occur. For example, "optionally substituted with..." means that the substitution may or may not occur.

[0038] When the term "each independently" is used in combination with "arbitrarily", for example, "each independently arbitrarily replaced by..." means that the specific options are replaced by... or not by... without affecting each other.

[0039] The term "substituted or unsubstituted" as used in the present invention, when used as a prefix of a group, means that the group contains cases where the group is substituted by the substituents described in the present invention and cases where the group is not substituted by the substituents described in the present invention. The substituents involved in "substitution" are conventional substituents in the art, such as but not limited to hydroxyl, cyano, nitro, amino, thiol, halogen, oxo, ester, alkyl, heteroalkyl, aryl, heteroaryl, cycloalkyl, heterocyclic, etc. These conventional substituents may be further substituted; the substituents involved in "substitution" may also be unconventional substituents in the art, and these unconventional substituents may be substituted group fragments formed by reasonable combinations of conventional substituents. The common point of these substituents is that they will not affect the process of the method described in the present invention.

[0040] The term "substituted" refers to one or more hydrogen atoms on a specific group being replaced by a specific substituent. The specific substituent is a substituent described above, or a substituent appearing in the embodiments. Unless otherwise specified, a substituted group may have a substituent selected from a specific group at any substitutable site of the group, and the substituent may be the same or different at each position, i.e., each substitution is independent of each other. It will be appreciated by those skilled in the art that the combinations of substituents contemplated by the present invention are those that are stable or chemically feasible.

[0041] The term "substituted or unsubstituted alkyl" refers to an alkyl group that is substituted or unsubstituted by a substituent described in the present invention. "Alkyl" or "alkyl group" refers to a carbon-containing, saturated, straight-chain or branched hydrocarbon group. In one embodiment, the alkyl group contains 1 to 6 carbon atoms, i.e., C 1-6 In another embodiment, the alkyl group contains 1-4 carbon atoms, i.e., C 1-4 Alkyl; In another embodiment, the alkyl group contains 1-3 carbon atoms, i.e., C 1-3 Alkyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, and the like.

[0042] The terms substituted unsubstituted alkoxy and substituted unsubstituted alkylamino refer to groups in which the substituted unsubstituted alkyl described herein and an oxygen atom or a nitrogen atom form an oxy group or a nitrogen group.

[0043] The term "substituted unsubstituted cycloalkyl" refers to cycloalkyl groups that are substituted or unsubstituted with substituents described herein. "Cycloalkyl" means a monovalent or polyvalent monocyclic, bicyclic or tricyclic ring system (e.g., a monocyclic ring such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, or a bicyclic ring including a spirocyclic, fused or bridged system (e.g., bicyclo[1.1.1]pentyl, bicyclo[2.2.1]heptyl, bicyclo[3.2.1]octyl or bicyclo[5.2.0]nonyl, decalinyl, etc.) containing carbon atoms, which may be fully saturated or contain one or more degrees of unsaturation, but may not have an aromatic ring. In one embodiment, the cycloalkyl group contains 3-6 carbon atoms, such as C 3-6 Saturated or partially unsaturated cycloalkyl. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclopentenyl, cyclohexenyl, and the like. In one embodiment, the saturated or partially unsaturated cycloalkyl is selected from: saturated monocyclic cycloalkyl, saturated bicyclic cycloalkyl, saturated tricyclic cycloalkyl, partially unsaturated monocyclic cycloalkyl, partially unsaturated bicyclic cycloalkyl, partially unsaturated tricyclic cycloalkyl.4-7 Cycloalkyl refers to a cycloalkyl group having 4 to 7 ring atoms. 3-6 Cycloalkyl refers to a cycloalkyl group having 3 to 6 ring atoms.

[0044] The term "substituted or unsubstituted heterocyclic group" refers to heterocyclic groups that are substituted or unsubstituted by substituents described in the present invention. "Heterocyclic group" refers to a saturated (i.e., "heterocycloalkyl") or partially unsaturated monovalent monocyclic or bicyclic group having 2, 3, 4, 5, 6, 7, 8 or 9 carbon atoms and one or more (e.g., one, two, three or four) heteroatom-containing groups selected from C(=O), O, S, S(=O), S(=O)2 and NR' in the ring, wherein R' represents a hydrogen atom or C 1-6 Alkyl or halo-C 1-6 Alkyl. The heterocyclic group can be connected to the rest of the molecule through any one of the carbon atoms or the nitrogen atom (if present). In particular, a 3-10 membered heterocyclic group is a group having 3-10 (e.g., 3-7, 4-6, or 5-6) carbon atoms and heteroatoms in the ring, such as, but not limited to, an oxirane group, an aziridine group, an azetidinyl group, an oxetanyl group, a tetrahydrofuranyl group, a dioxolyl group, a pyrrolidinyl group, a pyrrolidonyl group, an imidazolidinyl group, a pyrazolidinyl group, a pyrrolinyl group, a tetrahydropyranyl group, a piperidinyl group, a morpholinyl group, a dithianyl group, a thiomorpholinyl group, a piperazinyl group, or a trithianyl group.

[0045] The term "substituted or unsubstituted alkenyl" refers to alkenyl groups that are substituted or unsubstituted by substituents described in the present invention. "Alkenyl" means a linear or branched monovalent hydrocarbon group containing carbon atoms, wherein at least one unsaturated site, i.e., one carbon-carbon sp2 double bond, including "cis" and "tans" orientations, or "E" and "Z" orientations. In one embodiment, the alkenyl group contains 2-6 carbon atoms, i.e., C 2-6 In another embodiment, the alkenyl group contains 2-4 carbon atoms, i.e., C 2-4 Alkenyl. Examples of alkenyl groups include, but are not limited to, vinyl (-CH=CH2), allyl (-CH2CH=CH2), and the like.

[0046] The term "substituted or unsubstituted alkynyl" refers to alkynyl groups that are substituted or unsubstituted with substituents described herein. "Alkynyl" means a linear or branched monovalent hydrocarbon group containing carbon atoms, wherein at least one unsaturated site, i.e., a carbon-carbon sp triple bond. In one embodiment, the alkynyl group contains 2-6 carbon atoms, i.e., C2-6 Alkynyl; In another embodiment, the alkynyl group contains 2-4 carbon atoms, i.e. C2-C4 alkynyl. Examples of alkynyl groups include, but are not limited to, ethynyl (-C≡CH), propargyl (-CH2C≡CH), 1-propynyl (-C≡C-CH3), and the like.

[0047] The term "substituted or unsubstituted aryl" refers to aryl groups that are substituted or unsubstituted by substituents described in the present invention. "Aryl" or "aromatic ring" refers to monocyclic, bicyclic, tricyclic aromatic carbocyclic ring systems. The term "aryl" can be used interchangeably with the term "aromatic ring" or "aromatic ring". 6-10 membered aryl refers to an aryl group containing 6-10 ring atoms. Examples include, but are not limited to, phenyl, naphthyl, etc.

[0048] The term "substituted or unsubstituted heteroaryl" refers to heteroaryl groups that are substituted or not substituted by substituents described in the present invention. "Heteroaryl" or "heteroaromatic ring" means a monocyclic, bicyclic and tricyclic aromatic system containing heteroatoms, and the term "heteroaryl" can be used interchangeably with the term "heteroaromatic ring" or "heteroaromatic compound". The heteroatoms have the definition described in the present invention. In some embodiments, the heteroaryl group is a heteroaryl group composed of 5-10 atoms containing 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 5-10-membered heteroaryl group; the heteroaryl group is a heteroaryl group composed of 5-8 atoms containing 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 5-8-membered heteroaryl group; in some embodiments, the heteroaryl group is a heteroaryl group composed of 5-7 atoms containing 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 5-7-membered heteroaryl group. ; In some embodiments, the heteroaryl group is a heteroaryl group consisting of 5-6 atoms comprising 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 5-6 membered heteroaryl group; In some embodiments, the heteroaryl group is a heteroaryl group consisting of 5 atoms comprising 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 5-membered heteroaryl group; In some embodiments, the heteroaryl group is a heteroaryl group consisting of 6 atoms comprising 1, 2, 3 or 4 heteroatoms independently selected from O, S and N, i.e., a 6-membered heteroaryl group. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Image of TiO2 (B) nanosheets with two-dimensional ultrathin flake structure characterized by transmission electron microscopy (TEM).

[0050] Figure 2 X-ray powder diffraction (XRD) was used to characterize the phase diagram of TiO2(B).

[0051] Figure 3 Low-resolution TEM characterization of two-dimensional Pd1 / TiO2 images.

[0052] Figure 4 Characterization of the two-dimensional Pd1 / TiO2 pattern by X-ray powder diffraction (XRD).

[0053] Figure 5 Characterization of two-dimensional Pd1 / TiO2 images by transmission microscopy (HAADF-STEM).

[0054] Figure 6 Characterization of the two-dimensional Pd1 / TiO2 image by in situ carbon monoxide adsorption infrared (CO-FTIR).

[0055] Figure 7 Characterization of the two-dimensional Pd1 / TiO2 map by X-ray near-edge structure (XANES).

[0056] Figure 8 To characterize the two-dimensional Pd1 / TiO2 map by extended edge X-ray absorption structure (EXAFS).

[0057] Fig. 9 This is a two-dimensional diagram of the action mechanism of Pd1 / TiO2; (A) The site where the catalyst dissociates hydrogen is at the Pd single atom; (B) Hydrogen is heterolytically split (H2=H++H-); (C) The substrate does not need to be activated at the Pd1 site, but is activated through H tunneling.

[0058] Fig.10 This is a diagram of the catalytic results of Example 1. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to constitute any limitation of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concepts of the present disclosure. Such structures and technologies are also described in many publications.

[0060] The reagents used in the present invention can be purchased from the market or prepared by the method described in the present invention. Preparation of catalyst:

[0061] 1. Preparation of TiO2(B) nanosheets

[0062] 1 mL of TiCl4 was added to 30 mL of ethylene glycol, and the resulting clear, transparent light yellow liquid was transferred to a hydrothermal autoclave lined with polytetrafluoroethylene, heated at 120 °C for 4 h, then naturally cooled to room temperature, washed by centrifugal alcohol, and dried at 60 °C overnight to obtain TiO2 (B) nanosheets.

[0063] Transmission electron microscopy (TEM) characterizes TiO2(B) nanosheets as two-dimensional ultrathin sheet structures, such as Figure 1 , X-ray powder diffraction (XRD) characterized it as TiO2 (B) phase, such as Figure 2 , the corresponding JCPDS card number is #074-1940.

[0064] 2. Preparation of catalyst

[0065] Atomic-level dispersed Pd atoms (two-dimensional Pd1 / TiO2) loaded on TiO2(B) with a loading amount of 0.5wt% were prepared by weighing 20mg of the TiO2(B) nanosheets obtained above and ultrasonically dispersing them into 10mL of water in a 50mL beaker. During magnetic stirring, an H2PdCl4 aqueous solution (containing 0.1mg Pd) was added and ultrasonically dispersed for 30s. The mixture was then exposed to ultraviolet light for 1h during magnetic stirring. The two-dimensional Pd1 / TiO2 catalyst was obtained by centrifugation, water washing and vacuum drying.

[0066] Characterization:

[0067] (i) Low-resolution TEM characterization shows that TiO2(B) has not changed and no Pd species can be seen, indicating that the Pd species may be dispersed in single atoms, such as Figure 3 .

[0068] (ii) XRD characterization shows that only the crystalline phase of the carrier TiO2 (B) exists, but no crystalline phase of the Pd species, which also indicates that the Pd species may be dispersed in single atoms, such as Figure 4 .

[0069] (iii) High-angle annular dark-field scanning transmission microscopy (HAADF-STEM) characterization demonstrated that the Pd species were atomically dispersed, e.g. Figure 5 .

[0070] (iv) In situ carbon monoxide adsorption infrared (CO-FTIR) characterization showed that CO adsorbed on the catalyst surface existed at 2016-2095 cm -1 The absorption peak of -1 , corresponding to the top-site adsorption of CO on the positively charged Pd atom, without bridge or hole adsorption, proving the atomic dispersion of Pd, and further proving that the atomically dispersed Pd atoms are not zero-valent, but have positive charges, such as Figure 6 .

[0071] (v) X-ray near-edge structure (XANES) characterization shows that the Pd element is between zero valence and positive divalence (relative to zero valence Pd metal film and PdO standard), such as Figure 7 .

[0072] (vi) Extended edge X-ray absorption structure (EXAFS) characterization shows that there are only Pd-O bonds but no Pd-Pd bonds in Pd1 / TiO2, proving that the Pd element is atomically dispersed and chemically bonded to the surface of the carrier TiO2 (B) through Pd-O-Ti bonds and is in a positive valence state, such as Figure 8 .

[0073] Catalytic Reaction Example

[0074] Selectively catalyze the hydrogenation of aromatic aldehydes and ketones to aromatic alcohol compounds. Disperse the obtained 10 mg two-dimensional Pd1 / TiO2 catalyst in 5 mL of reaction solvent (e.g., methanol). Set the reaction temperature (e.g., 30°C), set the H2 pressure (e.g., 0.1 MPa), add the substrate (taking 1 mmol of benzaldehyde as an example, the molar ratio of Pd to benzaldehyde is 1:2129), and react under sufficient stirring. The conversion rate and selectivity are measured by gas chromatography (GC) and 1 H nuclear magnetic resonance (NMR) detection.

[0075] The reaction solvent may be water, alcohol (methanol, ethanol, isopropanol and tert-butanol, etc.), tetrahydrofuran, etc., or a mixed solvent (such as a mixed solvent of water and methanol).

[0076] The reaction temperature ranges from 0 to 60° C., preferably 30° C. The reaction temperature is not limited and depends on the freezing point and boiling point of the solvent used.

[0077] The H2 pressure may be 0.05-0.5 MPa, preferably 0.1 MPa. The reaction pressure is not limited and is subject to the tolerable pressure of the reactor used.

[0078] The molar ratio of Pd to the aromatic aldehyde and ketone compound in the catalyst can be 1:(10-10000), preferably 1:2000.

[0079] The aromatic aldehyde and ketone compound has the structure described in formula (I);

[0080]

[0081] Among them, R 1 is selected from: H and substituted or unsubstituted alkyl;

[0082] R 2 is selected from H, halogen, hydroxyl, mercapto, cyano, amino, nitro, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkylamino, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkenyl and substituted or unsubstituted alkynyl; optionally, two adjacent R 2, together with the atoms to which they are attached, form a substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl or substituted or unsubstituted heterocyclyl;

[0083] X 1 , X 2 , X 3 , X 4 and X 5 are independently CH or N; X 1 , X 2 , X 3 , X 4 and X 5 Not all are N;

[0084] n is selected from 0, 1, 2, 3, 4 or 5.

[0085] The aromatic aldehyde and ketone compound has a structure as described in formula (II);

[0086]

[0087] R 1 is H or alkyl; preferably, the alkyl is selected from: methyl, ethyl or propyl;

[0088] R 2 is H, hydroxyl, halogen, alkyl or alkoxy; preferably, the alkyl is selected from: methyl, ethyl or propyl; the alkoxy is selected from: methoxy or ethoxy.

[0089] Mechanism of action:

[0090] The catalyst of the present invention dissociates hydrogen at a single Pd atom (active site such as Fig. 9 (A)), hydrogen is heterolytic (H2=H++H-), the structure after hydrogen dissociation is as follows Fig. 9 (B) Instead of homolytic cleavage (H2=2·H), the dissociation of hydrogen in the patent is homolytic activation at Pd nanoparticles, and its two-dimensional Pd1 / TiO2 single-atom catalyst lacks effective H2 molecule dissociation sites. The substrate of the present invention does not need to be activated at the Pd1 site, but is activated by H tunneling. See the mechanism diagram Fig. 9 (C).

[0091] Embodiment 1:

[0092] 10 mg of the obtained two-dimensional Pd1 / TiO2 catalyst was dispersed in 5 mL of methanol, the reaction temperature was 30 °C, the H2 pressure was set to 0.1 MPa, 1 mmol of benzaldehyde was added, and the reaction was carried out under sufficient stirring. Within 70 min, the benzaldehyde was completely converted to benzyl alcohol, and no by-product toluene was generated. Even if the reaction time was extended to 120 min, the selectivity could be maintained, as shown in Table 1 and Fig.10shown.

[0093] Table 1

[0094] Time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 10 15 100 20 33 100 30 51 100 40 68 100 50 86 100 60 99 100 70 100 100 80 100 100 90 100 100 100 100 100 110 100 100 120 100 100

[0095] The catalytic stability test showed that the catalyst had good catalytic stability, which was manifested in that the catalyst could complete six catalytic reactions without any decrease in activity, as shown in Table 2.

[0096] Table 2

[0097] Number of applications Reaction time (min) Benzaldehyde transfer rate (%) Benzyl alcohol selectivity (%) 1 30 70 100 2 30 71 100 3 30 72 100 4 30 69 100 5 30 71 100 6 30 71 100

[0098] Example 2

[0099] The difference between this embodiment and embodiment 1 is the difference in the solvent used, which can be one of water, ethanol, isopropanol, tert-butanol and tetrahydrofuran, and the conversion of the substrate can be completed in 20 minutes in an aqueous solution, in 50 minutes in an ethanol or isopropanol solution, in 110 minutes in a tert-butanol solution, and in 120 minutes in a tetrahydrofuran solution, as shown in Table 3. In addition, in a mixed solution of methanol and water, the addition of water can significantly increase the reaction rate, as shown in Table 4.

[0100] Table 3

[0101] Solvents Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) water 15 99 100 Ethanol 60 99 100 Isopropyl alcohol 60 100 100 Tert-Butanol 120 100 100 Tetrahydrofuran 120 99 100

[0102] Table 4

[0103]

[0104] Example 3

[0105] The difference between this embodiment and embodiment 2 is that the acidity and alkalinity of the aqueous solution used are different. The acidity and alkalinity (pH) of the 5 mL aqueous solution used is adjusted by introducing hydrochloric acid and sodium hydroxide. The pH values ​​used are 1, 3, 5, 9, 11 and 13. The catalytic activity of the catalyst is not greatly affected by the pH and has good acid-base tolerance. See Table 5.

[0106] Table 5

[0107] pH Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 1 60 98 100 3 60 99 100 5 60 100 100 9 60 100 100 11 60 97 100 13 60 98 100

[0108] Example 4

[0109] The difference between this example and Example 1 is the different reaction temperatures used, the temperature range used is 0-60°C, the temperature has little effect on the reaction rate, indicating that the activation energy of the reaction is small, the reactions at different temperatures can complete the substrate conversion in 70 minutes, and the selectivity for benzyl alcohol is approximately 100%. The results are shown in Table 6.

[0110] Table 6

[0111] Reaction temperature (℃) Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 60 30 100 100 50 40 100 100 40 50 100 100 30 60 100 100 20 60 100 100 10 70 100 100 0 70 100 100

[0112] Example 5

[0113] The difference between this embodiment and embodiment 1 is the different H2 pressures used. The H2 pressure range is 0.05-0.5 MPa. The higher the pressure, the faster the reaction rate. The reactions under different H2 pressures can complete the substrate conversion in 80 min, and the selectivity for benzyl alcohol is approximately 100%. The results are shown in Table 7.

[0114] Table 7

[0115] <![CDATA[H2 pressure (MPa)]]> Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 0.05 80 100 100 0.1 60 100 100 0.2 40 100 100 0.3 30 100 100 0.4 20 100 100 0.5 10 100 100

[0116] Example 6

[0117] The difference between this embodiment and embodiment 1 is that the molar ratio of Pd to the substrate is different. The molar ratio of Pd to the substrate used is in the range of 1:(100-1000). The relationship between the reaction rate and the molar ratio of Pd to the substrate has a volcano-shaped curve. When the molar ratio of Pd to the substrate is 2000, the reaction rate is the fastest. The results are shown in Table 8.

[0118] Table 8

[0119] Pd: substrate Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 1:500 15 100 100 1:1000 25 100 100 1:2000 25 100 100 1:4000 60 100 100 1:6000 100 100 100 1:10000 200 100 100

[0120] Example 7

[0121] The difference between this embodiment and embodiment 1 is that the Pd loading in the catalyst used is different, and the loading used can be 0.1-1.5wt%, and the specific experimental test is 0.1wt%, 0.25wt%, 0.75wt%, 1.0wt%, 1.5wt%. Given enough reaction time, the benzaldehyde conversion rate and benzyl alcohol selectivity are close to 100%. The results are shown in Table 9.

[0122] Table 9

[0123] Loading amount (wt%) Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) 0.1 300 100 100 0.25 120 100 100 0.75 40 100 100 1.0 30 100 100 1.5 20 100 100

[0124] Example 8

[0125] The difference between this embodiment and embodiment 1 is that the substrates used are different, and the substrates used include benzaldehyde and phenyl ketones containing substituents. The conversion rate and selectivity results of various substrates are shown in Table 10.

[0126] Table 10

[0127]

[0128]

[0129] Comparative Example 1

[0130] The difference between this embodiment and embodiment 1 lies in the different catalysts used. The catalysts used are commercial Pd / C catalysts or H2PdCl4. As shown in Table 11, the catalytic activities of both are relatively poor. After the reaction is carried out for 100 min, the conversion rate of benzaldehyde is less than 10%.

[0131] Table 11

[0132] catalyst Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) Pd / C 20 1 100 Pd / C 40 2 100 Pd / C 60 3 100 Pd / C 80 4 100 Pd / C 100 5 100 <![CDATA[H2PdCl4]]> 20 1 100 <![CDATA[H2PdCl4]]> 40 2 100 <![CDATA[H2PdCl4]]> 60 3 100 <![CDATA[H2PdCl4]]> 80 4 100 <![CDATA[H2PdCl4]]> 100 5 100

[0133] Comparative Example 2

[0134] The difference between this embodiment and embodiment 1 is the different solvents used, which are acetonitrile, toluene, cyclohexane, dioxane and chloroform. Among the above solvents, the activity of the catalyst is relatively poor. After the reaction is carried out for 120 minutes, the conversion rate of benzaldehyde is less than 5%. See Table 12.

[0135] Table 12

[0136] Solvent Name Reaction time (min) Benzaldehyde conversion rate (%) Benzyl alcohol selectivity (%) Acetonitrile 120 4 100 Toluene 120 3 100 Cyclohexane 120 2.5 100 Dioxane 120 3.5 100 Chloroform 120 4 100

[0137] Comparative Example 3

[0138] The difference between this embodiment and embodiment 1 is that the substrates used are different. The substrates used are fatty aldehydes and ketones, such as n-valeraldehyde, 2-phenylacetaldehyde, acetone and cyclohexanone, etc. The activity of the catalyst in catalyzing the selective hydrogenation of the above substrates is relatively poor. After the reaction is carried out for 100 minutes, the substrate conversion rate is less than 2%. The results are shown in Table 13.

[0139] Table 13

[0140] Substrate name Reaction time (min) Conversion rate (%) Selectivity (%) n-Valeraldehyde 100 1 100 2-Phenylacetaldehyde 10 1.2 100 acetone 100 1.5 100 Cyclohexanone 100 0.5 100

[0141] The method of the present invention has been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein within the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention.

Claims

1. A catalyst for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, characterized in that: The catalyst is atomically dispersed Pd atoms supported by TiO2(B), the TiO2(B) is an ultra-thin two-dimensional structure, and the Pd loading is 0.1wt% to 1.5wt%.

2. A method for preparing a catalyst for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, characterized in that: Includes steps: (1) Preparation of TiO2(B) nanosheets: TiCl4 was added to ethylene glycol, and the resulting clear and transparent liquid was heated at 120°C for 4 hours, cooled, washed with ethylene glycol by centrifugation, and dried to obtain TiO2(B) nanosheets; wherein the volume ratio of ethylene glycol to TiCl4 was 30:1; (2) The TiO2 (B) nanosheets obtained above are ultrasonically dispersed in water, and H2PdCl4 aqueous solution is added under stirring. Ultrasonic dispersion, stirring and ultraviolet irradiation for 1 hour, centrifugation, water washing and vacuum drying can obtain a two-dimensional Pd1 / TiO2 catalyst; wherein the mass ratio of TiO2 (B) nanosheets to Pd in ​​H2PdCl4 is (1000~65):

1.

3. Use of the catalyst according to claim 1 or the catalyst prepared by the preparation method according to claim 2 in selectively catalyzing the hydrogenation of aromatic aldehydes and ketones to obtain aromatic alcohols.

4. A method for selectively catalyzing the hydrogenation of aromatic aldehydes and ketones, characterized in that: The method comprises dispersing a two-dimensional Pd1 / TiO2 catalyst in a solvent, adding aromatic aldehydes and ketones to react at a certain temperature and a certain H2 pressure to obtain aromatic alcohols as hydrogenation products of the aromatic aldehydes and ketones; the two-dimensional Pd1 / TiO2 catalyst is the catalyst described in claim 1 or 2 or the catalyst prepared by the preparation method described in claim 3.

5. The method according to claim 4, characterized in that The reaction solvent is selected from one or more of water, alcohol, and tetrahydrofuran; preferably, the reaction solvent is selected from one or more of water, methanol, ethanol, isopropanol, tert-butanol, and tetrahydrofuran.

6. The method according to claim 4, characterized in that The aromatic aldehyde and ketone compounds are selected from one or more of substituted or unsubstituted aromatic aldehydes and substituted or unsubstituted aromatic ketones.

7. The method according to claim 4, characterized in that The aromatic aldehyde and ketone compound has a structure as described in formula (I); Among them, R 1 is selected from H and substituted or unsubstituted alkyl; R 2 is selected from H, halogen, hydroxyl, mercapto, cyano, amino, nitro, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkylamino, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkenyl and substituted or unsubstituted alkynyl; optionally, two adjacent R 2 , together with the atoms to which they are attached, form a substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl or substituted or unsubstituted heterocyclyl; X 1 , X 2 , X 3 , X 4 and X 5 are independently CH or N; X 1 , X 2 , X 3 , X 4 and X 5 Not all are N; n is selected from 0, 1, 2, 3, 4 or 5.

8. The method according to claim 4, characterized in that The aromatic aldehyde and ketone compound has a structure as described in formula (II); R 1 is H or alkyl; preferably, the alkyl is selected from methyl, ethyl or propyl; R 2 is H, hydroxyl, halogen, alkyl or alkoxy; preferably, the alkyl is selected from methyl, ethyl or propyl; the alkoxy is selected from methoxy or ethoxy.

9. The method according to claim 4, characterized in that The reaction temperature is selected based on the freezing point and boiling point of the solvent used; the reaction pressure is based on the tolerance pressure of the reactor used.

10. The method according to claim 4, characterized in that The molar ratio of Pd to aromatic aldehyde and ketone compounds in the two-dimensional Pd1 / TiO2 catalyst can be 1:(10-10000); preferably 1:2000.

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