Systems and methods are provided for using a high heat capacity gas as at least a portion of the diluent during the regeneration step of a reverse flow reactor process. Instead of using nitrogen or air as the primary diluent gas, CO.sub.2 and/or H.sub.2O can be added as diluent gas for the regeneration step in the reaction cycle. Increasing the heat capacity of the diluent gas provides a reduction in the peak temperature within the reactor relative to the amount of fuel combusted during regeneration. This can allow for a reduction in the volume of diluent used during regeneration and/or an increase in the amount of fuel used. Reducing the volume of diluent can reduce the pressure drop during regeneration, which can provide a corresponding reduction in the amount of compression required for recycle of the diluent. Increasing the amount of fuel can allow for a corresponding increase in the amount of endothermic reaction performed during the reaction step.

Photoactive catalyst and methods of producing H.sub.2 by photocatalytic water splitting. The photoactive catalyst includes an upconverting material, a photocatalyst material, and plasmonic metal nanostructures deposited on the surface of the photocatalyst material. The upconverting material is not embedded in or coated by the photocatalyst material. The upconverting material is capable of emitting light at a first wavelength that has an energy equal to or higher than the band gap of the photocatalyst material and at a second wavelength that can be absorbed by the plasmonic metal nanostructures.

A catalytic membrane reactor and methods of operating and producing the same are provided that efficiently produces highly pure hydrogen (H.sub.2) from ammonia (NH.sub.3) as well as operates according to other chemical conversion processes. In one embodiment, a tubular ceramic support made from porous yttria-stabilized zirconia has an outer surface that is impregnated with a metal catalyst such as ruthenium and then plated with a hydrogen permeable membrane such as palladium. An inner surface of the ceramic support is impregnated with cesium to promote conversion of ammonia to hydrogen and nitrogen (N.sub.2). The resulting catalytic membrane reactor produces highly pure hydrogen at low temperatures and with less catalytic loading. Therefore, ammonia can be used to effectively transport hydrogen for use in, for example, fuel cells in a vehicle.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

The present disclosure provides methods for fabricating catalysts for ammonia decomposition. The method may comprise (a) subjecting a catalyst support to one or more physical or chemical processes to optimize one or more pores, morphologies, and/or surface chemistry or property of the catalyst support; (b) depositing a composite support material on the catalyst support, wherein the composite support material comprises a morphology or surface chemistry or property; and (c) depositing one or more active metals on at least one of the composite support material and the catalyst support, wherein the one or more active metals comprise one or more nanoparticles configured to conform to the morphology of the composite support material and/or catalyst support material, thereby optimizing one or more active sites on the nanoparticles for ammonia processing.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

The invention relates to a method and to a plant for chemical looping oxidation-reduction combustion (CLC) of a gaseous hydrocarbon feed, for example natural gas essentially containing methane. According to the invention, catalytic steam reforming of the feed is performed between two successive feed combustion steps on contact with an oxidation-reduction active mass in form of particles. The reforming catalyst is arranged in a fixed bed in an intermediate reforming zone (130) between the two reduction zones (120, 140) where the two combustion steps are conducted.

In a method and a plant for chemical looping oxidation-reduction combustion (CLC) of a gaseous hydrocarbon feed, for example natural gas essentially containing methane, catalytic reforming of the feed is performed within the reduction zone where combustion of the feed is conducted on contact with an oxidation-reduction active mass in form of particles. The reforming catalyst comes in form of untransported fluidized particles within the reduction zone. The catalyst thus confined in the reduction zone does not circulate in the CLC loop.

In general, disclosed herein are methods for forming hydrogen by use of an ammonia decomposition catalyst system. For instance, a method can include contacting a catalyst system with an ammonia source at a temperature of about 450? C. or lower. The catalyst systems can include a support material and a trimetallic catalyst component carried on the support material and within a reactor. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

A method for enriching a synthesis gas in hydrogen is presented. The method includes adding H.sub.2O to the synthesis gas to form a synthesis gas stream that includes hydrogen, carbon monoxide, and steam. The synthesis gas stream has a steam to dry gas molar ratio, S/DG; and an oxygen to carbon molar ratio, O/C. The method includes introducing the synthesis gas stream into a water-gas shift reactor and reacting the synthesis gas stream in the water-gas shift reactor in the presence of a non-iron-based catalyst to produce a shifted synthesis gas. The method further includes controlling an outlet temperature of the synthesis gas stream to remain at or below a critical temperature or to drop to or below the critical temperature by adjusting the S/DG ratio to maintain the O/C ratio below a lower O/C limit or above an upper O/C limit.