Selection of heterogeneous catalysts with metallic surface states

Abstract

The present invention relates to a method for controlling a catalyst having at least one metal surface state, comprising: a) identifying all topological insulators in an ICSD, b) calculating the real-space invariants of the valence bands of all these topological insulators, and c) identifying the Wyckoff positions where the irreducible Wannier charge centers are concentrated in all these topological insulators, and then d) selecting a topological insulator as a potential catalytically active compound: wherein the WCC position is not occupied by any atom; e) synthesizing a crystal of the selected potential catalytically active compound so that it grows in a predetermined crystallographic direction (characterized by its Miller indices (h, k, l)) that exposes the metal surface state; or cutting the crystal in a predetermined crystallographic direction (characterized by its Miller indices (h, k, l)) to expose the metal surface state, wherein the predetermined crystallographic direction is the direction of the normal vector (h, k, l) of the surface plane f(x, y, z) = 0, the plane passing through the position blocking the WCC but leaving the atomic position, and its condition is satisfied when (l), wherein the blocking WCC is concentrated in #imgabs0# and the atom occupies WP occ ={x i ,y i ,z i |i∈occupies the position}. #imgabs1#

Description

Background Art

[0001] Heterogeneous catalytic reactions such as photocatalytic / electrochemical water splitting (HER / OER), ammonia synthesis, CO2 reduction, and oxygen reduction reaction (ORR) in fuel cells are gaining increasing attention due to their advantages in addressing energy crises and environmental issues. With the help of these technologies, hydrogen can be generated from water and then used directly in fuel cells without any pollutant emissions. CO2 and N2 can be converted into specific carbon products or ammonia, which are important for industry and fertilizers. Unfortunately, all these reactions require corresponding catalysts to reduce the activation energy for large-scale production. The design and search for high-performance catalysts strongly rely on understanding the details of the catalytic reactions and the physical properties of the catalysts. Currently, d-band theory (J. et al. (PNAS, 2011, 108, 937; L. Pettersson et al. Top. Catal. 2014, 57, 2) have achieved great success in explaining the catalytic efficiency of selected catalysts. Within the framework of d-band theory, reaction kinetics are determined by the adsorption energy between reaction intermediates and the catalyst's active sites. However, fundamental and unanswered questions remain why adsorption energies vary for different crystal surfaces of the same catalyst and how the active sites of a selected catalyst can be determined.

[0002] Transition metal dichalcogenides such as MoS2 are potential alternatives to noble metal-based catalysts due to their high catalytic efficiency and stability. Experimentally, it has been well demonstrated that the (001) basal plane of MoS2 crystals is inert to the catalytic process of photocatalytic / electrochemical water splitting reactions. The edges of the crystals act as active sites (see Figure 1 Only when defects, such as elemental vacancies, are introduced into the basal planes can they be activated for catalysis. Similar phenomena have been observed in other materials such as PtSe2, PtTe2, and PdTe2. However, it remains unclear why catalytic efficiency varies significantly across different crystal surfaces of the same catalyst and what factors determine adsorption energy. This is crucial for designing new, high-performance catalysts.

[0003] Existing technology

[0004] US20140353166A1 discloses methods for the large-scale synthesis of molybdenum disulfide monolayer and few-layer films. When deposited on SiO2 / Si substrates and used as electrocatalysts for hydrogen evolution, they exhibit high efficiency, large exchange current density, and low Tafel slope. The reference states that monolayer and few-layer films have more active sites than nanoparticles and bulk phases.

[0005] WO2018165449A1 discloses the formation of molybdenum disulfide nanosheets on a carbon fiber substrate. These nanosheets have multiple catalytically active edge sites along the basal surface and show good activity for hydrogen evolution.

[0006] JP2009252412A relates to the use of RuTe2 as an active component for direct methanol fuel cells. Fuel cells with RuTe2 as a catalyst can be used in portable electrical products.

[0007] M. Asadi, K. Kim, C. Liu, AV Addepalli, P. Abbasi, P. Yasaei, P. Phillips, A. Behranginia, J. M. Cerrato, R. Haasch, P. Zapol, B. Kumar, RF Klie, J. Abiade, LA Curtiss, and A. Salehi-Khojin (Science, 2016, 353, 467) reported that nanostructured transition metal dichalcogenides such as MoS2, WS2, MoSe2, and WSe2 are excellent electrocatalysts for CO2 reduction. The authors found that the metallic edge sites of the nanosheets are active centers due to strong bonding with CO molecules.

[0008] C.Tsai, K.Chan, F.Abild-Pedersen, JK (Phys.Chem.Chem.Phys.2014,16,13156), TF Jaramillo, KP J. Bonde, JH Nielsen, S. Horch, Ib Chorkendorff (Science, 2007, 317, 100), R. Abinaya, J. Archana, S. Harish, M. Navaneethan, S. Ponnusamy, C. Muthamizhchelvan, M. Shimomura, and Y. Hayakawa (RSCA Adv., 2018, 8, 26664) reported that the photocatalytic and electrochemical efficiencies of transition metal dichalcogenides (MoS2) are related to the number of edge sites in the crystal, while the (001) basal plane of MoS2 crystals is inert to hydrogen evolution.

[0009] H. Li, M. Du, M. J. Mleczko, A. Koh, Y. Nishi, E. Pop, A. J. Bard and X. Zheng (J. Am. Chem. Soc. 2016, 138, 5123); S. Kang, S. Han, Y. Kang (Chem Sus Chem, 2019, 12, 2671); L. Zeng, S. Chen, J. van der Zalm, X. Li, A. Chen (Chem. Commun., 2019, 55, 7386) found that the catalytic activity of MoS2 in hydrogen evolution reaction, CO2 reduction and NH3 synthesis can be improved by introducing sulfur vacancies in the (001) basal plane of MoS2 crystals.

[0010] A.Politano, G.Chiarello, C.Kuo, C.Lue, R.Edla, P.Torelli, V.Pellegrini, DWBoukhvalov (Adv.Funct.Mater.2018,28,1706504), H.Huang, X.Fan, DJSingh and W.Zheng (ACS Omega2018,3,10058) found that the original surface of layered transition metal dichalcogenides (PtSe2, PtTe2) is chemically inert to the most common ambient gases including O2, HO, and even in air. However, by doping or introducing selenium or tellurium vacancies, a large density of active sites can be generated in the (001) basal plane for water splitting and water-gas shift reactions.

[0011] Despite all these efforts, it is still not understood what active site(s) are used for various catalytic processes. For example, it is not understood why the adsorption energy can be significantly changed by introducing defects such as vacancies. The answers to these questions are very important for designing high-performance catalysts with controllable active sites for given heterogeneous reactions.

[0012] Purpose of the Invention

[0013] Therefore, the object of the present invention is to provide

[0014] - a method for controllably preparing a catalyst having active surface site(s), and / or

[0015] - a method for improving the efficiency of known catalysts which have hitherto not been able to make available their most active surface site(s);

[0016] - A catalyst exhibiting active surface site(s), as determined by the above method.

[0017] Brief Description of the Invention

[0018] By using the Inorganic Crystal Structure Database, FIZ Karlsruhe, Germany (ICSD, https: / / icsd.fiz-karlsruhe.de ) To achieve the above object, topological insulators, in particular topological trivial insulators, are selected in which the position of the WCC (Wannier charge center) is not occupied by an atom. These compounds are characterized by a metallic surface state at a predetermined specific crystal surface determined by the method according to the present invention. In order to expose the metallic surface state to potential reactants of the photocatalytic / electrochemical reaction, crystals of the selected insulating compound are cut or grown in a predetermined crystallographic direction (characterized by its Miller indices (h, k, l)).

[0019] Found that the given has the WP occ ={x i ,y i ,z i The atoms and the positions occupied by |i∈ The blocking atomic insulator (OAI) of a blocking WCC has a metallic surface state on the surface plane, characterized by the equation f(x,y,z)=0 with Miller indices (or normal vectors) (h,k,l) ​​when it satisfies the following conditions:

[0020]

[0021] This means that the surface plane f(x,y,z)=0 with normal vector (h,k,l) ​​cuts through the position (X j ,Y j ,Z j ), but keep leaving the atomic position (x i ,y i ,z i ).

[0022] Topological trivial insulators are those insulators without topological electronic structure, characterized by an indirect band gap (about 0.001-7.000 eV) in the bulk, in which the conduction band and the valence band have different crystal momenta (k-vectors). Using the real-space invariants (RSIs) disclosed in topological quantum chemistry theory (Nature 547.7663 (2017): 298-305) and "Science 367 (6479), 794-797 (2020)", it was found that some topological insulators, particularly topological trivial insulators, have metallic surface states protected by crystallographic symmetry on specific crystalline surfaces and found that these metallic surface states can explain catalytic performance.

[0023] Thus, the present invention may provide new and / or improved catalysts, in particular for photocatalytic / electrochemical reactions such as water splitting (oxygen evolution reaction OER or hydrogen evolution reaction HER), ammonia synthesis, CO2 reduction, and the oxygen reduction reaction (ORR) in fuel cells.

[0024] Detailed Description of the Invention

[0025] It was found that the active sites of heterogeneous reactions are metallic surface states, concentrated at / on specific crystal surfaces, characterized by their surface normals expressed as (h, k, l)-indices (Miller indices). Metallic surface states can be imagined as "dangling bonds" extending from the surface of the catalyst and causing metallic conductivity. Within the crystal (bulk) of the catalytic compound, all bonds are saturated; the atomic orbitals (AO) of the elements that make up the catalytic compound overlap with each other, thereby forming molecular orbitals (MO) with associated electrons. However, at the boundaries of the crystal, some atomic orbitals do not have corresponding binding partners for forming MO; they remain "unsaturated" and extend beyond the grain boundaries as "dangling bonds". Of course, metallic surface states or "dangling bonds" can also be produced by introducing defects such as element vacancies in the crystal structure. It was found that the metallic surface states defined above improve catalytic efficiency. Therefore, using the knowledge found above, technicians can

[0026] a) explain the catalytic efficiency of known catalytic compounds,

[0027] b) transforming a given compound with still unrevealed catalytic potential into an effective catalyst by cutting or growing a crystal of the potential catalytic material in a predetermined crystallographic direction (characterized by its surface normal, expressed as Miller indices (h, k, l)), thereby revealing metallic surface states. The directions are determined by the crystal surface with metallic surface states, which can be calculated from the following material list (see below) or obtained

[0028] c) using the method b) to ultimately improve the catalytic efficiency of a known catalytic compound,

[0029] d) screening known compounds for catalytic materials, and / or

[0030] e) Provide a list of compounds that can be used as catalysts.

[0031] As used herein, the following terms have the following meanings:

[0032] "Surface properties" means the bonding and electronic structure at the surface of a crystal.

[0033] "Topologically trivial insulator" means an insulator according to the conventional definition, i.e., an insulator without topological feature(s) such as band inversion between conduction and valence bands. Thus, insulators that exhibit (a) topological feature(s) are called "topological insulators."

[0034] "Indirect band gap" means that the bottom of the conduction band and the top of the valence band have different crystal momenta (k-vectors) in the Brillouin zone.

[0035] "Metallic surface states" refer to electronic states derived from dangling bonds that lie between the conduction and valence bands. These surface states have delocalized electrons and are highly conductive. In real space, they are at the crystal surface. In momentum space (k), they reside in the gap between the bulk conduction and valence bands.

[0036] By "some surface" is meant a surface of a catalyst crystal having a surface normal with assigned Miller indices ((h, k, l)-indices).

[0037] "Catalytically active site" refers to the surface of a crystal where heterogeneous catalytic reactions can occur.

[0038] "Occupied position" means the available Wyckoff position in a given space group occupied by (one or more) atoms. Examples are given below for space group 25 (Pmm2):

[0039] Wyckoff position of group Pmm2 (number 25)

[0040]

[0041]

[0042] Thus, the Wyckoff positions of a defined space group consist of all points X for which the site symmetry group is a conjugate subgroup of the defined space group. Each Wyckoff position of a space group is labeled by a letter known as a Wyckoff letter. The number of different Wyckoff positions for each space group is finite, with a maximum of 9 for plane groups (implemented in p2mm) and 27 for space groups (implemented in Pmmm). There are a total of 72 Wyckoff positions in plane groups and 1731 Wyckoff positions in space groups.

[0043] Heterogeneous catalysis is a type of catalytic process in which the catalyst and reactants are not present in the same phase. This occurs, for example, in reactions between gases or liquids, or both, at the surface of a solid catalyst. Typical heterogeneous catalytic reactions include photocatalytic / electrochemical water splitting, ammonia synthesis, CO2 reduction, and the oxygen reduction reaction (ORR) in fuel cells. According to classical surface adsorption theory, heterogeneous reactions consist of four stages:

[0044] 1) The reactants diffuse to the surface of the solid catalyst. The diffusion rate is determined by the bulk concentration of the reactants and the thickness of the boundary layer surrounding the catalyst particles (the solution layer formed at the catalyst surface).

[0045] 2) The reactants are adsorbed onto the catalyst surface through chemical or physical bonding.

[0046] 3) Oxidation or reduction at the catalyst surface, characterized by electron transfer between the catalyst and the adsorbate.

[0047] 4) Desorption of reaction products: When the product(s) desorb from the catalyst surface, the process is accompanied by the breaking of the bond(s).

[0048] The efficiency of the catalysis generally depends on the adsorption energy of the adsorbate / reaction intermediate and the catalytically active site(s). A good catalyst requires an adsorption energy that is "just right" so that the product can be formed and released as quickly as possible. The adsorption energy can be positive or negative; a positive energy means weak adsorption, while a negative energy means good, i.e., strong adsorption. However, an adsorption energy that is too positive will lead to a low concentration of reactants at the catalyst surface(s) and will therefore increase the reaction kinetics. On the other hand, if the adsorption energy is too negative, the product stays on the catalyst surface for too long and can act as a "poison" for the active site(s).

[0049] The catalytic efficiency of topological insulators, particularly topologically trivial insulators, has been found to be directly related to their metallic surface states. Using topological quantum chemistry (TQC) theory (Nature 547.7663 (2017): 298-305), they confirmed the existence of all topologically trivial and non-trivial band insulators in the Inorganic Crystal Structure Database (ICSD) (Nature 566.7745 (2017): 480-485). Topologically trivial insulators are divided into two distinct categories: those with and those without surface states.

[0050] The valence bands of all these topological band insulators are confirmed in the band representation (BR) (see: Nature 566.7745) (2017): 480-485; and in the Topological Materials Database, see: https: / / www.topologicalquantumchemi stry.com ). For WP with location in Wyckoff occ ={x i ,y i ,z iFor a given topological band insulator of an atom with |i∈occ=occupied position}, one can calculate the RSI for all Wyckoff positions (WP) of the crystal symmetry group using, for example, the formula for BR and real-space invariants (RSI) disclosed in "Science 367(6479), 794-797(2020)". Thus, for a given space group, one can define the RSI for each Wyckoff position of that space group. For topological band insulators, the RSI defined at a Wyckoff position is always an integer, representing the number of irreducible Wannier orbitals (=irreducible Wannier charge centers (WCCs)) at that Wyckoff position.

[0051] Wyckoff positions with nonzero RSI yield positions of irreducible Wannier charge centers (WCCs) (Physical Review B 89.11(2014)), WP wcc ={x k ,y k ,z k RSI k ≠0}. Any BR of a topological band insulator with at least one irreducible WCC concentrated in an empty Wyckoff site (i.e., a Wyckoff site not occupied by an atom) is in the blocking atom confined phase, i.e. Therefore, all Wyckoff sites that have a non-zero RSI and are not occupied by atoms of the material are called "blocked Wyckoff sites". A band insulator is an unblocking atomic insulator when all its irreducible WCCs are occupied by atoms. Otherwise, it is a blocking atomic insulator (OAI).

[0052] For Wyckoff position WP with occupancy occ ={x i ,y i ,z i |i∈occupied position} and blocked Wyckoff position The blocking atomic insulators have a surface plane with Miller index (or normal vector) (h, k, l) f(x, y, z) = 0 and a metallic surface state when (h, k, l) satisfies the following conditions:

[0053]

[0054] This means that the surface plane f(x,y,z)=0 with normal vector (h,k,l) ​​cuts through positions blocking the Wyckoff position, but remains clear of occupied positions in the crystal.

[0055] Any cleaved crystal surface that cuts through these blocked Wyckoff positions must have metallic surface states on the crystal surface. The above theory can be used to predict the location of these metallic surface states on the catalyst crystal surface. This is in the case of MoS2 crystals. Figure 1 and 2 Surface states are located at edge sites with dangling bonds. The (001) basal plane has no surface states and is inert to catalytic reactions. However, edge sites orthogonal to the (001) plane, such as (100), (010), or (110), are active for catalytic reactions such as hydrogen evolution. When these metallic surface states are located near the Fermi level (i.e., below or above the Fermi level by up to about 0.5 eV), they can be easily transferred during catalytic reactions and can serve as active centers for chemical reactions.

[0056] exist Figure 3 The position of the metallic surface states in the MoS2 crystal is shown in Figure 2. MoS2 crystallizes in the space group P63 / mmc (#194), where Mo and S are at the Wyckoff positions 2c (1 / 3, 2 / 3, 1 / 4) and 4f (1 / 3, 2 / 3, z) (where z is a general position not equal to 1 / 4), respectively. Using topological quantum chemistry (TQC) theory, the real space invariant (RSI) of the Wyckoff position 2b (0, 0, 1 / 4) is δ(b) = 1.0. Therefore, there is an irreducible WCC concentrated at the 2b position that is not occupied by atoms. This shows that using the above theory, technicians can confirm that there is a Wyckoff position as in Figure 3 The surface planes in MoS2 are shown in (a) as metallic surface states (indicated by their Miller indices (1,0,0)). On the other hand, a surface with Miller indices (0,0,1) cuts through the 2c sites occupied by atoms. Thus, as Figure 3 As shown in (b), the (001) surface does not have a metallic surface state within the energy gap.

[0057] The predicted catalytic behavior of MoS2 crystals has been experimentally demonstrated. Figure 4 The experimental setup showing HER. Bulk MoS2 single crystal is connected to a silver-coated titanium wire. Figure 4 The edges and base are clearly visible. Figure 5 a shows the linear polarization curves for the entire crystal (edge ​​+ basal plane) and the edge and basal plane alone. It can be seen that the activity of the entire crystal is almost identical to that of the edge. The activity decreases significantly when the edge is partially covered by gel. Figure 5 b shows an image taken at an overpotential of -0.57 relative RHE. Hydrogen bubbles form at the edges but not on the basal plane. Therefore, it can be concluded that the HER activity originates from the crystal edges.

[0058] Therefore, the present invention provides a method for selecting a latent catalytically active compound, the method comprising

[0059] - identify all topological insulators in the ICSD, preferably all topologically trivial insulators,

[0060] - Compute the real-space invariants of the valence bands of all these topological insulators so that

[0061] - confirm the Wyckoff location of the irreducible Wannier charge centers (WCCs) in all these topological insulators, and then

[0062] - Topological insulators were selected as potential catalytically active compounds, in which the WCC sites are not occupied by any atoms.

[0063] This method was applied to all compounds in the ICSD and potentially catalytically active compounds were identified. These compounds are listed in the attached table labeled "OAI." Many compounds in this table have multiple listings. Multiple listings for the same compound (meaning the same stoichiometry) can occur when different factors in the ICSD report (slightly) varying data, such as varying lattice parameters, different space group assignments, or Wyckoff assignments. A concise list of unique compounds (= only one listing) is reproduced in Table 1 below:

[0064] Table 1

[0065]

[0066]

[0067]

[0068]

[0069] In one aspect of the present invention, a method is provided for controllably preparing a catalyst having active surface site(s), the method comprising

[0070] - Selecting a potentially catalytically active compound according to the above selection process or from Table 1 above,

[0071] - synthesizing a crystal of the potentially catalytically active compound such that it is either grown in a predetermined crystallographic direction (characterized by its h, k, 1-indices) that exposes metallic surface states; or cutting the crystal in a predetermined crystallographic direction (characterized by its h, k, 1-indices) such that the metallic surface states are exposed,

[0072] The predetermined crystallographic direction is the direction of the normal vector (h, k, 1) of the surface plane f(x, y, z) = 0, which cuts through the position blocking the WCC but leaves the atomic position, and its conditions are met when:

[0073]

[0074] Among them, the blocking WCC is concentrated and Atom Occupy WP occ ={x i ,y i , z i |the position occupied by i∈}.

[0075] Additional aspects of the present invention include methods for converting the following into a compound providing a surface having metallic surface states by cutting or growing a crystal of the compound in a predetermined crystallographic direction, thereby revealing the metallic surface states, wherein the predetermined crystallographic direction is determined as described above,

[0076] - a compound, which

[0077] Either use the above method to select or

[0078] o Select from Table 1,

[0079] - and the compound does not provide a surface having a metallic surface state

[0080] In addition, the present invention comprises a catalyst selected from the compounds listed in Table 1

[0081] - wherein crystals of the selected compound are grown in predetermined crystallographic directions (characterized by their h, k, l-indices); or are cut in predetermined crystallographic directions (characterized by their h, k, l-indices),

[0082] - where the predetermined crystallographic direction is the direction of the normal vector (h,k,l) ​​of the surface plane f(x,y,z)=0, which plane cuts through the site blocking the WCC, but leaves the atomic site, and its conditions are met when:

[0083]

[0084] Among them, the blocking WCC is concentrated and Atom Occupy WP occ ={x i ,y i ,z i |the position occupied by i∈}.

[0085] Methods for preparing compounds

[0086] The compounds of the present invention can be grown, for example, from a stoichiometric mixture of the elements of the compound. The elements can be mixed together and then heated, preferably to a temperature of about 300°C, preferably 200°C, and most preferably 100°C, greater than the melting point of the lowest melting point element, for a period of 1 to 10 hours, preferably 2 to 8 hours, more preferably 3 to 7 hours, and then maintained at that temperature for 5 to 50 hours, preferably 10 to 30 hours, and more preferably about 20 hours. Preferably, the mixture is placed in an inert crucible for heating, such as an alumina crucible, which is preferably sealed, such as a quartz tube under a partial pressure of an inert gas such as Ar. Thereafter, the mixture is slowly cooled to a temperature of about 450°C, preferably 400°C, and more preferably 350°C, for a period of 40 to 90 hours, preferably 50 to 80 hours, and more preferably 55 to 65 hours.

[0087] In an alternative method, a polycrystalline ingot is first prepared from a stoichiometric mixture of elements, for example using induction or arc melting techniques. The ingot is then crushed into a microcrystalline powder and preferably packed into an alumina tube with tapered ends, which is then completely sealed in a tantalum tube. The tube is then heated to a temperature above the melting point of the compound to achieve a fully molten state, and then slowly cooled to approximately 650°C and then to room temperature.

[0088] In general, compounds are manufactured so that they grow in a predetermined crystallization direction (characterized by its (h, k, l)-index) exposing metallic surface states. The morphology of known crystals is closely related to the surface energy of each crystal surface. In the crystal growth process, the crystal surface with high surface energy has a faster growth rate than the lower surface energy. Therefore, according to thermodynamic equilibrium theory, those surfaces with high surface energy will disappear and the surface with the lowest total energy will be spared (M.Khan et al. CrystEngComm, 2013, 15, 2631). Therefore, if the metallic surface state meets the surface with the lowest surface energy, technicians can design catalysts. If the metallic surface state is located at the crystal surface with high surface energy, surface energy can be controlled by using additives. Additives such as polyvinyl pyrrolidone, sodium lauryl sulfate and hypophosphorous acid can be combined with specific crystallization surfaces and reduce surface energy. This will reduce the crystal growth rate and change the morphology, thereby exposing the desired crystal surface with metallic surface state (JP van der Eerden et al. Electrochim. Acta, 1986, 31, 1007; A. Ballabh et al. Cryst. Growth Des., 2006, 6, 1591). It is also possible to "cut" the crystal in a predetermined crystallization direction (characterized by its h, k, l-index) so that the metallic surface state is exposed. For the catalyst in the form of bulk crystals, crystal structure and crystal orientation can be determined by single crystal X-ray diffraction. After determining the orientation, the technician can cut the crystal in the direction of the specification and expose the desired crystal surface.

[0089] OAI table

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Claims

1. A method for preparing a catalyst having at least one metallic surface state, comprising: a) Identify all topological insulators in ICSD, b) Compute the real-space invariants of the valence bands of all these topological insulators so that c) Identify the Wyckoff locations of the irreducible Wannier charge centers, or WCCs, in all these topological insulators, and then d) Selecting a topological insulator as a potentially catalytically active compound: wherein the Wyckoff sites of the WCC are not occupied by any atoms of the topological insulator, wherein the Wyckoff sites of the WCC not occupied by any atoms correspond to Wyckoff sites that block the WCC, i.e., WP OAI , e) synthesizing a crystal of the selected potentially catalytically active compound, either by growing it in a predetermined crystallographic direction characterized by its Miller indices (h, k, l) such that said at least one metallic surface state is exposed; or by cutting the crystal in a predetermined crystallographic direction characterized by its Miller indices (h, k, l) such that said at least one metallic surface state is exposed, The predetermined crystallographic direction is the direction of the normal vector (h, k, l) of the surface plane f(x, y, z) = 0, which cuts through the Wyckoff position blocking the WCC, i.e., the WP. OAI , but leaves the Wyckoff position of the selected atoms of the topological insulator, which corresponds to the occupied Wyckoff position, i.e. WP OCC , which satisfies its conditions when: The blocking WCC is concentrated in and the atoms of the selected potentially catalytically active compounds occupy WP occ ={x i ,y i ,z i |the position occupied by i∈}.

2. The method according to claim 1, wherein the topological insulator is a topologically trivial insulator.

3. The process according to claim 1 , wherein instead of steps a) to d), the latent catalytically active compound is selected from the list consisting of:

4. A method of converting a compound to provide a surface having at least one metallic surface state, the compound being selected by a method comprising: a. Confirm all topological insulators in ICSD, b. Compute the real-space invariants of the valence bands of all these topological insulators so that c. Identify the Wyckoff locations of the irreducible Wannier charge centers (WCCs) in all these topological insulators, and then d. Select such topological insulators as potential catalytically active compounds: in which the Wyckoff sites of the WCC are not occupied by any atoms of the topological insulator, where the Wyckoff sites of the WCC not occupied by any atoms correspond to the Wyckoff sites that block the WCC, i.e., WP OAI , or, It is selected from the list consisting of: and the compound does not provide a surface having at least one metallic surface state, which is achieved by cutting or growing a crystal of the compound in a predetermined crystallographic direction to reveal the at least one metallic surface state, wherein the predetermined crystallographic direction is the direction of the normal vector (h, k, l) of the surface plane f(x, y, z) = 0, which plane cuts through the Wyckoff position blocking the WCC, i.e., the WP OAI , but leaves the Wyckoff position of the selected atoms of the topological insulator, which corresponds to the occupied Wyckoff position, i.e. WP OCC , which satisfies its conditions when: The blocking WCC is concentrated in and the atoms of the selected potentially catalytically active compounds occupy WP occ ={x i ,y i ,z i |the position occupied by i∈}.

5. The method according to any one of claims 1 to 4, wherein the topological insulator compound is characterized by an indirect band gap in the bulk of 0.001 to 7.000 eV.

6. The method of any one of claims 1 to 4, wherein the metal surface states are located within 0.3 to 0.7 electron volts above or below the Fermi level.

7. The method of claim 6, wherein the metallic surface states are located within 0.4 to 0.6 eV above or below the Fermi level.

8. The method of claim 6, wherein the metal surface states are located about 0.5 eV above or below the Fermi level.

9. Catalyst selected from the list consisting of the following compounds: - wherein crystals of the selected compound are grown in predetermined crystallographic directions characterized by their h, k, l-indices; or cut in predetermined crystallographic directions characterized by their h, k, l-indices, - wherein the predetermined crystallographic direction is the direction of the normal vector (h, k, l) of the surface plane f(x, y, z) = 0, which plane cuts through the Wyckoff position blocking the WCC, i.e., the WP OAI , but leaves the Wyckoff position of the selected atoms of the topological insulator, which corresponds to the occupied Wyckoff position, i.e. WP OCC , which satisfies its conditions when: - - where the blocking WCC is concentrated and the atoms of the selected potentially catalytically active compounds occupy WP occ ={x i ,y i ,z i |the position occupied by i∈}.

10. Use of a compound according to claim 9 or a compound obtained by a process according to claim 1 or 4 as a catalyst for water splitting, ammonia synthesis, CO2 reduction and oxygen reduction reactions in fuel cells.

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