BACKGROUND

Methane is the most abundant organic compound on earth, and it is the main constituent of natural gas (typically more than 90%). To date, a few large-scale commercial gas-to-liquid plants have been in operation (Ref. 1, Ex. 1) but they are based on an indirect route and complex Fischer-Tropsch technology with high capital costs. To be competitive, these plants rely on low cost natural gas and high crude oil prices (significantly higher than the current crude oil prices of approximately $40 per barrel).

Direct conversion of methane to higher value chemicals (e.g., ethylene) would be much more cost-effective. (Refs. 2, 3, Ex. 1) Ethylene is a major hydrocarbon building block in industry; (Ref. 4, Ex. 1) its worldwide production was over 150 million tonnes in 2016, which exceeds that of any other man-made organic compound. Currently, ethylene is produced from crude oil in a multistep high-temperature (˜950° C.) process (Ref. 5, Ex. 1), and is the largest contributor to greenhouse gas emissions in the chemical industry. Therefore, the ability to use methane as the raw material in the production of ethylene, fuels and other higher value chemicals would be highly advantageous due to the abundance of low cost, domestic natural gas, (Ref. 6, Ex. 1) and the potential for using biogas in the future.

These needs and other needs are satisfied by the present disclosure.

SUMMARY

In accordance with the purpose(s) of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to a single-atom-based catalyst system with single-atom catalytic sites in a controlled hierarchical structure over length scales ranging from macroscopic dimensions down to atomic scales, the single-atom-based catalyst system comprising: at least one catalyst structure comprising a first assembly of a plurality of single-atom-catalyst superparticles, further comprising a second assembly of a plurality of single-atom-catalyst nanoparticles.

According to one aspect, each of the single-atom-catalyst nanoparticles comprises a core-shell support structure having a crystalline metal oxide support surface, and one or more single-atom catalysts anchored to the support surface, wherein the density and location of the single-atom catalysts on the support surface are controlled within a 20% variance to provide a highly uniform spatial distribution of single-atom catalysts. Further, each of the second assemblies is a sub-micron-sized superlattice of a plurality of the single-atom-catalyst nanoparticles, the superlattice having a second density and a second porosity, wherein the second density is controlled within a 20% variance to provide a single-atom-catalyst superparticle having a precise porosity and a highly uniform spatial distribution of the single-atom catalysts. The first assembly of single atom-catalyst superparticles has a first density and a first porosity, wherein the first density of the first assembly is controlled within a 10% variance to provide a catalyst structure having a precise porosity and highly uniform spatial distribution of the single-atom catalysts. Optionally, the single-atom-based catalyst system can comprise one or more catalytically-inactive support materials.

According to some aspects, a tandem catalyst structure can comprise: a first catalyst layer comprising a first catalyst structure; and a second catalyst layer in fluid communication with the first catalyst layer, said second catalyst layer comprising a second catalyst structure. Optionally, the first catalyst layer, the second catalyst layer, or both can comprise a support layer comprising a catalytically inactive supporter material that supports the respective catalyst structure and/or a spacer layer.

According to additional aspects, a method for three-dimensional printing a single-atom-based catalyst system, such as those described herein, can comprise: providing a first ink substrate comprising a plurality of positively-charged first single-atom-catalyst superparticles; providing a second ink substrate comprising a plurality of positively-charged second single-atom-catalyst superparticles; providing a support ink substrate comprising a plurality of catalytically inactive supporter particles; providing a binder ink substrate comprising a plurality of negatively-charged polymeric binders; and selectively depositing with a 3D printing apparatus each of the first ink substrate, the second ink substrate, the support substrate, and the binder ink substrate to provide the elements of the single-atom-based catalyst system.

According to additional aspects, a method of converting methane to ethylene can comprise providing a single-atom-based catalyst system as described herein, wherein the single-atom-based catalyst system has a first catalyst layer comprising a first catalyst for the oxidative coupling of methane (OCM) into ethane and a second catalyst layer comprising a second catalyst for the oxidative dehydration of ethane (ODE) to ethylene; wherein the method comprises: introducing a first fluid comprising methane to the single-atom-based catalyst system; passing the first fluid through the first catalyst layer so that at least a portion of the methane contacts the first single-atom catalyst structure, providing a first reaction product comprising ethane; passing the first reaction product through the second catalyst layer so that at least a portion of the ethane contacts the second single-atom catalyst structure, providing a second reaction product comprising ethylene; and withdrawing the second reaction product from the single-atom-based catalyst system.

Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

