EP-4737000-A1 - MACROPOROUS SILICON MONOLITH AND METHOD FOR PRODUCING A MACROPOROUS SILICON MONOLITH

Abstract

A macroporous silicon monolith and a method for producing a macroporous silicon monolith are provided. The macroporous silicon monolith comprises a silicon substrate (7) including, on a surface (8) thereof, a structure of hollow silicon oxide tubes (14), the latter being functionalized with catalytic and/or photocatalytic materials (16).

Inventors

• GUPTA, Yash
• LLORCA PIQUE, JORDI
• RODRÍGUEZ MARTÍNEZ, Ángel
• VEGA BRU, DIDAC

Assignees

• Universitat Politècnica De Catalunya

Dates

Publication Date

20260506

Application Date

20241105

Claims (15)

1. A macroporous silicon monolith, comprising a silicon substrate (7) including, on a surface (8) thereof, a structure of hollow silicon oxide tubes (14), the latter being functionalized with catalytic and/or photocatalytic materials (16).
2. The macroporous silicon monolith of claim 1, wherein the catalytic and/or photocatalytic materials (16) comprise inorganic oxide micro and/or nanoparticles.
3. The macroporous silicon monolith of claim 1 or 2, wherein the structure of hollow silicon oxide tubes (14) comprises a coating (15) of a photocatalyst material, wherein the catalytic and/or photocatalytic materials (16) are deposited or impregnated over said coating (15).
4. The macroporous silicon monolith of claim 3, wherein the photocatalyst material comprises a semiconductor oxide including titanium oxide (TiO 2 ).
5. The macroporous silicon monolith of any one of the previous claims, wherein a base of the structure of hollow silicon oxide tubes (14) comprises one or more reflective layers (18).
6. The macroporous silicon monolith of any one of the previous claims, wherein the catalytic and/or photocatalytic materials (16) are selected among titanium dioxide and/or noble metal particles including platinum, gold, and/or palladium.
7. The macroporous silicon monolith of any one of the previous claims, wherein a diameter of the hollow silicon oxide tubes (14) is modulated in depth.
8. The macroporous silicon monolith of any one of the previous claims, wherein the hollow silicon oxide tubes (14) are interconnected through bridges (17).
9. The macroporous silicon monolith of any one of the previous claims, wherein the structure of hollow silicon oxide tubes (14) is sealed with a transparent element (23) comprising a plurality of openings (32) for the entry of reactants (3) and exit of reaction products (28).
10. A method for producing a macroporous silicon monolith, the method comprising: providing a macroporous silicon sample comprising a silicon substrate; producing on a surface of the silicon substrate a structure of silicon oxide tubes via a porosification and oxidation process; and functionalizing the structure of silicon oxide tubes with catalytic and/or photocatalytic materials.
11. The method of claim 10, wherein the porosification and oxidation process comprises a light-assisted electrochemical etching or a reactive ion etching.
12. The method of claim 10 or 11, further comprising coating the structure of silicon oxide tubes with a layer of a photocatalyst material, the inorganic catalytic and/or photocatalytic materials being deposited or impregnated over said layer.
13. The method of any one of the previous claims 10-12, further comprising providing one or more reflective layers over a base of the structure of silicon oxide tubes.
14. The method of any one of the previous claims 10-13, further comprising sealing the structure of silicon oxide tubes with a transparent material comprising a plurality of openings for the entry of reactants and exit of reaction products.
15. The method of any one of the previous claims 10-14, further comprising modulating a diameter of the hollow silicon oxide tubes in depth.

Description

TECHNICAL FIELD The present invention relates to support structures for catalytic and photocatalytic materials (monoliths) and their production methods. In particular, the invention relates to a macroporous silicon monolith and to a method for production thereof. BACKGROUND OF THE INVENTION Catalytic monoliths are devices that contain a catalytic material which promotes and/or accelerates a chemical reaction, making them widely used in various chemical processes across different industries. Thus, catalytic devices used in different industries can have a monolithic geometry. The use of support structures for catalysts has a long history in industry. For instance, WO2012136971A1 describes general structures and shapes used in catalytic converters in industry. The patent application highlights some issues that arise, particularly when using large structures, such as mechanical rigidity and strength, proper temperature control (uniformity, regulation, etc.), and pressure losses in the system. The type of structures they describe are metal-based tubular systems (mainly stainless steel), designed for large-scale industries, with sizes reaching lengths of up to 20 meters and diameters of up to 40 millimeters. These structures typically operate with gas flows in a laminar regime, which necessitates long tubes. Reducing the length leads to smaller catalysts, easing the mechanical loads. WO2006016966A2 proposes the use of structures with channels in more than one direction, allowing the gas to flow in a turbulent regime, thereby slowing it down and increasing the interaction time with the catalytic particles, which allows for smaller monoliths. Other proposals include layering catalytic layers and separating membranes, such as in WO2012112046A1. In this case, several of these groups are concatenated, allowing control of the inlet gas flow and product gases through separating membranes. These structures are complex to build, and it is necessary to find a balance between the size of the catalytic particles and the channel dimensions. Another alternative for reducing total size is proposed in CN104258796B, where a structure of stainless steel capillary tubes wound in a spiral is described, achieving lengths of up to 300 meters. However, this structure faces challenges with gas passage due to the long tubes and small diameters. Other similar solutions can be cited, based on stacked or complex structures to reduce dimensions, such as WO2008076903A1. Regarding temperature control within reactors, US9441777B2 proposes the use of microreactors. These solutions are significantly smaller in size, even suitable for personal applications. Likewise, US9475026, aims to control the distribution of gases in microreactors to achieve a uniform flow. Examples of microreactors include US007714274B2, using silicon, or CN101052463B. Another relevant example is WO2005094983A2, which describes microreactors on an alumina substrate, both employing micromachining techniques to fabricate these monoliths. Lastly, emerging manufacturing techniques based on 3D printing have also been developed. For example, WO2018052287A1, which utilizes standard equipment to deposit, layer by layer, a catalyst-loaded paste, forming channels through which the reaction gases flow. Similarly, WO2018099957A1 creates fibers instead of channels. The great advantage of 3D printing is that it allows the design of monoliths with virtually free geometries, as demonstrated in US11389765B2, where the monolith takes the form of a minimal surface, specifically a gyroid. This geometry combines the idea of turbulent flow in the manufacturing process to extend residence time and improve conversion. Despite the evident advantages of 3D printing, it has significant limitations. On the one hand, the selection of materials may be restricted, as well as the dimensions and precision achievable with standard techniques. There are more precise methods, such as microstereolithography projection, though they face greater size limitations. Additionally, it should be noted that 3D printing techniques are inherently slow and not easily scalable. In order to reduce operating temperatures, other studies propose alternative methods to supply reaction energy beyond thermal energy, specifically using light as an energy source: photocatalysis. In the study "Dynamic photocatalytic hydrogen production from ethanol-water mixtures in an optical fiber honeycomb reactor loaded with Au/TiO2", Elena Taboada et al., Journal of Catalysis, 309 (January 2014), 460-467, the evolution of hydrogen production from ethanol via photocatalysis using optical fibers inserted into typical cordierite monoliths is analyzed. Similarly, the articles "Effect of temperature on the gas-phase photocatalytic H2 generation using microreactors under UVA and sunlight irradiation", Alejandra Castedo et al. Fuel, 222 (June 2018), 327-333, and "Kinetic analysis and CFD simulations of the photocatalytic production of hydrogen in silic