In U.S. Patent 7632774, Headwaters Technology Innovation, LLC (Lawrenceville, NJ) divulges a method for manufacturing supported nanocatalysts with an acid-functionalized support useful in the direct synthesis of hydrogen peroxide.
According to inventors Michael A. Rueter, Sukesh Parasher, Cheng Zhang, and Bing Zhou, supported catalysts include an inorganic solid support such as silica that is functionalized to have inorganic acid functional groups attached thereto. The functionalization of the support material is optimized by (i) limiting the amount of water present during the functionalization reaction, (ii) using a concentrated mineral acid or derivative thereof, and/or (iii) increasing the reaction temperature and/or reaction pressure. The acid-functionalized support material serves as a support for a metal nanoparticle catalyst. The nanocatalyst particles are preferably bonded to the support material through an organic molecule, oligomer, or polymer having functional groups that can bind to both the nanocatalyst particles and to the support material. The supported catalysts can advantageously be used for the direct synthesis of hydrogen peroxide from hydrogen and oxygen feed streams.
The reaction conditions of step (iii) are optimized to produce a catalyst with a greater number of acid groups on the surface of the support while causing minimal degradation of the support material and/or improved catalyst performance in direct hydrogen peroxide synthesis.
The reaction conditions of step (iii) are optimized to produce a catalyst with a greater number of acid groups on the surface of the support while causing minimal degradation of the support material and/or improved catalyst performance in direct hydrogen peroxide synthesis.
Hydrogen peroxide is a commercially important product which is widely used in the textile industry, paper industry, and chemical industry as a bleaching agent, biocide, and chemical reagent. Traditionally, hydrogen peroxide has been manufactured through a process which includes multiple oxidation and reduction steps using alkylanthraquinones. This process is complicated and expensive because of the many steps involved, the large volumes of reagents, the relatively high cost of intermediates, and the production of inactive by-products.
Recently, efforts have been made to develop an alternative process whereby hydrogen peroxide is directly synthesized from hydrogen and oxygen using precious metal catalysts. The direct synthesis of hydrogen peroxide offers significant economic advantages because it avoids making intermediate products and does not need the use of reagents such as alkylanthraquinones.
One important aspect of a direct synthesis process is the catalyst, which must be able to selectively convert hydrogen and oxygen to hydrogen peroxide, with minimal production of water, a competing by-product that is thermodynamically favored over hydrogen peroxide. In general, catalysts for the direct synthesis reaction use palladium or a combination of palladium and platinum, as the active catalyst. These catalysts are generally used in the form of small particles dispersed on a solid catalyst support.
While catalysts formed from small particulates can advantageously have high activity, small particulates present a problem with attrition. Because of the high cost of the active catalyst metals, the metals need to be used efficiently and should be recoverable. In some cases, metal that separates from the support can be recovered in expensive filtration systems. However, many of the metal particles that separate from the support are too fine to be recovered in the filtration process and are thus unrecoverable. Modifying the support and/or the catalyst particles to reduce attrition is very difficult because the task must be accomplished without significantly effecting catalyst performance.
The nanocatalyst is particularly advantageous when used with metal oxides for the support material. Metal oxides often lack adequate bonding sites for bonding a catalyst as compared with other support materials. Providing acid functionalization compensates for the initial lack of bonding sites. Examples of suitable metal oxides include silica, alumina, natural and synthetic zeolites, among others.
Headwaters Technology catalysts are particularly advantageous for the direct synthesis of hydrogen peroxide from hydrogen and oxygen. The hydrogen peroxide promoting catalysts manufactured include a combination of palladium and platinum. In addition, the catalyst nanoparticles can be controllably formed to have a crystal face exposure. Suitable dispersing agents for producing catalyst nanoparticles with a crystal face exposure include linear polymers or oligomers, such as lower molecular weight polyacrylic acid. (e.g., between about 300 to about 15,000 Daltons).
Headwaters Technology catalysts can be used in any type of reactor suitable for the direct synthesis of hydrogen peroxide. Suitable reactors include fixed bed, ebullated bed, and slurry reactors. When the catalysts are loaded into a fixed bed or ebullated bed reactor for hydrogen peroxide production, the recovery and regeneration of the catalyst is facilitated.
Recently, efforts have been made to develop an alternative process whereby hydrogen peroxide is directly synthesized from hydrogen and oxygen using precious metal catalysts. The direct synthesis of hydrogen peroxide offers significant economic advantages because it avoids making intermediate products and does not need the use of reagents such as alkylanthraquinones.
One important aspect of a direct synthesis process is the catalyst, which must be able to selectively convert hydrogen and oxygen to hydrogen peroxide, with minimal production of water, a competing by-product that is thermodynamically favored over hydrogen peroxide. In general, catalysts for the direct synthesis reaction use palladium or a combination of palladium and platinum, as the active catalyst. These catalysts are generally used in the form of small particles dispersed on a solid catalyst support.
While catalysts formed from small particulates can advantageously have high activity, small particulates present a problem with attrition. Because of the high cost of the active catalyst metals, the metals need to be used efficiently and should be recoverable. In some cases, metal that separates from the support can be recovered in expensive filtration systems. However, many of the metal particles that separate from the support are too fine to be recovered in the filtration process and are thus unrecoverable. Modifying the support and/or the catalyst particles to reduce attrition is very difficult because the task must be accomplished without significantly effecting catalyst performance.
The nanocatalyst is particularly advantageous when used with metal oxides for the support material. Metal oxides often lack adequate bonding sites for bonding a catalyst as compared with other support materials. Providing acid functionalization compensates for the initial lack of bonding sites. Examples of suitable metal oxides include silica, alumina, natural and synthetic zeolites, among others.
Headwaters Technology catalysts are particularly advantageous for the direct synthesis of hydrogen peroxide from hydrogen and oxygen. The hydrogen peroxide promoting catalysts manufactured include a combination of palladium and platinum. In addition, the catalyst nanoparticles can be controllably formed to have a crystal face exposure. Suitable dispersing agents for producing catalyst nanoparticles with a crystal face exposure include linear polymers or oligomers, such as lower molecular weight polyacrylic acid. (e.g., between about 300 to about 15,000 Daltons).
Headwaters Technology catalysts can be used in any type of reactor suitable for the direct synthesis of hydrogen peroxide. Suitable reactors include fixed bed, ebullated bed, and slurry reactors. When the catalysts are loaded into a fixed bed or ebullated bed reactor for hydrogen peroxide production, the recovery and regeneration of the catalyst is facilitated.
