Effect of Metal Complexing on Mn–Fe/TS-1 Catalysts for Selective Catalytic Reduction of NO with NH3

TS-1 zeolite with desirable pore structure, an abundance of acidic sites, and good thermal stability promising as a support for the selective catalytic reduction of NO with NH3 (NH3-SCR). Herein, a series of Mn–Fe/TS-1 catalysts have been synthesized, adopting tetraethylenepentamine (TEPA) as a metal complexing agent using the one-pot hydrothermal method. The introduced TEPA can not only increase the loading of active components but also prompts the formation of a hierarchical structure through decreasing the size of TS-1 nanocrystals to produce intercrystalline mesopores during the hydrothermal crystallization process. The optimized Mn–Fe/TS-1(R-2) catalyst shows remarkable NH3-SCR performance. Moreover, it exhibits excellent resistance to H2O and SO2 at low temperatures. The characterization results indicate that Mn–Fe/TS-1(R-2) possesses abundant surface Mn4+ and Fe2+ and chemisorbed oxygen, strong reducibility, and a high Brønsted acid amount. For comparison, Mn–Fe/TiO2 displays a narrower active temperature window due to its poor thermostability.

Highly Active Catalytic CO2 Hydrogenation to Lower Olefins via Spinel ZnGaOx Combined with SAPO-34

A key primary method for creating a carbon cycle and carbon neutrality is the catalytic hydrogenation of CO₂ into high value-added chemicals or fuels. In this work, ZnGaO_x oxides were prepared by parallel co-precipitation and physically mixed with SAPO-34 molecular sieves prepared by hydrothermal synthesis to produce ZnGaO_x /SAPO-34 bifunctional catalysts, which were evaluated for the catalytic synthesis of lower olefins (C₂ ⁼ -C₄ ⁼ ) from carbon dioxide hydrogenation. It was demonstrated that the reaction process requires oxygen defect activation, synergistic hydrogenation, and CO₂ alkaline adsorption of ZnGaO_x . The spinel structure of ZnGaO_x has more abundant oxygen defects and alkaline adsorption sites than the ZnGaO_x solid solution, which effectively enhances the catalytic performance. The CO₂ conversion was 28.52%, the selectivity of C₂ ⁼ -C₄ ⁼ in hydrocarbons reached 70.01%, and the single-pass yield of C₂ ⁼ -C₄ ⁼ was 10.95% at 370 °C, 3.0 MPa, and 4800 mL/g_cat /h.

Influence of the ZnCrAl Oxide Composition on the Formation of Hydrocarbons from Syngas

The conversion of syngas into value-added hydrocarbons gains increasing attention due to its potential to produce sustainable platform chemicals from simple starting materials. Along this line, the "OX-ZEO" process that combines a methanol synthesis catalyst with a zeolite, capable of catalyzing the methanol-to-hydrocarbon reaction, was found to be a suitable alternative to the classical Fischer-Tropsch synthesis. Hitherto, understanding the mechanism of the OX-ZEO process and simultaneously optimizing the CO conversion and the selectivity toward a specific hydrocarbon remains challenging. Herein, we present a comparison of a variety of ZnCrAl oxides with different metal ratios combined with a H-ZSM-5 zeolite for the conversion of syngas to hydrocarbons. The effect of aluminum on the catalytic activity was investigated for ZnCrAl oxides with a Zn/Cr ratio of 4:1, 1:1, and 1:2. The product distribution and CO conversion were found to be strongly influenced by the Zn/Cr/Al ratio. Although a ratio of Zn/Cr of 1:2 was best to produce lower olefins and aromatics, with aromatic selectivities of up to 37%, catalysts with a 4:1 ratio revealed high paraffin selectivity up to 52%. Notably, a distinct effect of aluminum in the oxide lattice on the catalytic activity and product selectivity was observed, as a higher Al content leads to a lower CO conversion and a changed product spectrum. We provide additional understanding of the influence of different compositions of ZnCrAl oxides on their surface properties and the catalytic activity in the OX-ZEO process. Furthermore, the variation of the zeolite component supports the important role of the channel topology of the porous support material for the hydrocarbon production. In addition, variation of the gas hourly space velocity showed a correlation of contact time, CO conversion, and hydrocarbon selectivity. At a gas hourly space velocity of 4200 mL/g_cat h, CO conversion as high as 44% along with a CO₂ selectivity of 42% and a lower paraffin (C₂ ⁰-C₄ ⁰) selectivity of 41% was observed.

Tandem Reactions over Zeolite-Based Catalysts in Syngas Conversion

Syngas conversion can play a vital role in providing energy and chemical supplies while meeting environmental requirements as the world gradually shifts toward a net-zero. While prospects of this process cannot be doubted, there is a lingering challenge in distinct product selectivity over the bulk transitional metal catalysts. To advance research in this respect, composite catalysts comprising traditional metal catalysts and zeolites have been deployed to distinct product selectivity while suppressing side reactions. Zeolites are common but highly efficient materials used in the chemical industry for hydroprocessing. Combining the advantages of zeolites and some transition metal catalysts has promoted the catalytic production of various hydrocarbons (e.g., light olefins, aromatics, and liquid fuels) and oxygenates (e.g., methanol, dimethyl ether, formic acid, and higher alcohols) from syngas. In this outlook, a thorough revelation on recent progress in syngas conversion to various products over metal-zeolite composite catalysts is validated. The strategies adopted to couple the metal species and zeolite material into a composite as well as the consequential morphologies for specific product selectivity are highlighted. The key zeolite descriptors that influence catalytic performance, such as framework topologies, proximity and confinement effects, acidities and cations, pore systems, and particle sizes are discussed to provide a deep understanding of the significance of zeolites in syngas conversion. Finally, an outlook regarding challenges and opportunities for syngas conversion using zeolite-based catalysts to meet emerging energy and environmental demands is also presented.

A Review on SAPO-34 Zeolite Materials for CO2 Capture and Conversion

Among several known zeolites, silicoaluminophosphate (SAPO)-34 zeolite exhibits a distinct chemical structure, unique pore size distribution, and chemical, thermal, and ion exchange capabilities, which have recently attracted considerable research attention. Global carbon dioxide (CO₂ ) emissions are a serious environmental issue. Current atmospheric CO₂ level exceeds 414 parts per million (ppm), which greatly influences humans, fauna, flora, and the ecosystem as a whole. Zeolites play a vital role in CO₂ removal, recycling, and utilization. This review summarizes the properties of the SAPO-34 zeolite and its role in CO₂ capture and separation from air and natural gas. In addition, due to their high thermal stability and catalytic nature, CO₂ conversions into valuable products over single metal, bi-metallic, and tri-metallic catalysts and their oxides supported on SAPO-34 were also summarized. Considering these accomplishments, substantial problems related to SAPO-34 are discussed, and future recommendations are offered in detail to predict how SAPO-34 could be employed for greenhouse gas mitigation.

Recent advances in biomass-derived platform chemicals to valeric acid synthesis

A perspective overview for levulinic acid and/or γ-valerolactone to valeric acid synthesis via thermocatalytic and electrocatalytic systems has been summarized.

Tunable Cu–M bimetal catalysts enable syngas electrosynthesis from carbon dioxide

Cu–M bimetal catalysts show excellent catalytic activity towards the CO2 reduction reaction.

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P₂O₅/SiO₂ and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al₂O₃:1.0 P₂O₅:1.2 DPA:0.3 SiO₂:120 H₂O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P₂O₅/SiO₂ molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m²/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.

Advances in Catalytic Applications of Zeolite-Supported Metal Catalysts

Zeolites possessing large specific surface areas, ordered micropores, and adjustable acidity/basicity have emerged as ideal supports to immobilize metal species with small sizes and high dispersities. In recent years, the zeolite-supported metal catalysts have been widely used in diverse catalytic processes, showing excellent activity, superior thermal/hydrothermal stability, and unique shape-selectivity. In this review, a comprehensive summary of the state-of-the-art achievements in catalytic applications of zeolite-supported metal catalysts are presented for important heterogeneous catalytic processes in the last five years, mainly including 1) the hydrogenation reactions (e.g., CO/CO₂ hydrogenation, hydrogenation of unsaturated compounds, and hydrogenation of nitrogenous compounds); 2) dehydrogenation reactions (e.g., alkane dehydrogenation and dehydrogenation of chemical hydrogen storage materials); 3) oxidation reactions (e.g., CO oxidation, methane oxidation, and alkene epoxidation); and 4) other reactions (e.g., hydroisomerization reaction and selective catalytic reduction of NO_x with ammonia reaction). Finally, some current limitations and future perspectives on the challenge and opportunity for this subject are pointed out. It is believed that this review will inspire more innovative research on the synthesis and catalysis of zeolite-supported metal catalysts and promote their future developments to meet the emerging demands for practical applications.

Oxide-Zeolite-Based Composite Catalyst Concept That Enables Syngas Chemistry beyond Fischer-Tropsch Synthesis

Syngas chemistry has been under study since Fischer-Tropsch synthesis (FTS) was invented in the 1920s. Despite the successful applications of FTS as the core technology of coal-to-liquid and gas-to-liquid processes in industry, the product selectivity control of syngas conversion still remains a great challenge, particularly for value-added chemicals such as light olefins. Recent studies show that the catalyst design concept of OXZEO (oxide-zeolite-based composite) enables direct syngas conversion to mixed light olefins with a selectivity reaching 80% and to ethylene with a selectivity of 83% among hydrocarbons. They both well-surpass the limits predicated by the Anderson-Schultz-Flory model via the conventional FTS route (58% and 30%, respectively). Furthermore, this catalyst concept allows one-step synthesis of gasoline-range isoparaffins and aromatic compounds, which is otherwise not possible in conventional FTS. A rapidly growing number of studies demonstrate the versatility of this concept and may form a technology platform for utilization of carbon resources including coal, natural gas, and biomass via syngas to a variety of basic chemicals and fuels. However, the selectivity control mechanism is far from being understood. Therefore, we focus mainly on the catalytic roles of the bifunctionalities of OXZEO while reviewing the development of bifunctional catalysts for selective syngas conversion by taking syngas-to-light olefins as an example. With this, we intend to provide insights into the selectivity control mechanism of the OXZEO concept in order to understand the challenges and prospects for future development of much more active and more selective catalysts.

Syngas to light olefin synthesis over La doped ZnxAlyOz composite and SAPO-34 hybrid catalysts

La doped Zn_xAl_yO_z with SAPO-34 hybrid catalysts for syngas to light olefin synthesis showed higher CO conversion and light olefin selectivity.

Effects of preparation method and precipitant on Mn–Ga oxide in combination with SAPO-34 for syngas conversion into light olefins

Mn–Ga oxides were prepared by different methods and using different precipitants, and the co-precipitated Mn–Ga using NH₃·H₂O as a precipitant exhibits the best performance.

On the reaction mechanism of MnOx/SAPO-34 bifunctional catalysts for the conversion of syngas to light olefins

Methanol is a key reaction intermediate formed on MnOx that synergistically reacts with SAPO-34 to produce light olefins.

Lower olefins from methane: recent advances

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution.

The bibliography includes 346 references.

Syngas to light olefins conversion with high olefin/paraffin ratio using ZnCrOx/AlPO-18 bifunctional catalysts

Direct synthesis of light olefins from syngas (STO) using a bifunctional catalyst composed of oxide and zeolite has attracted extensive attention in both academia and industry. It is highly desirable to develop robust catalysts that could enhance the CO conversion while simultaneously maintain high selectivity to C2-C4 olefins. Herein, we report a bifunctional catalyst consisting of ZnCr binary oxide (ZnCrO_x) and low-Si AlPO-18 zeolite, showing both satisfying selectivity to C2-C4 olefins of 45.0% (86.7%, CO₂ free) and high olefin/paraffin ratio of 29.9 at the CO conversion of 25.2% under mild reaction conditions (4.0 MPa, 390 °C). By optimizing the reaction conditions, the CO conversion could be markedly increased to 49.3% with a slight drop in selectivity. CD₃CN/CO-FTIR characterizations and theoretical calculations demonstrate that low-Si AlPO-18 zeolite has lower acid strength, and is therefore less reactive toward the hydride transfer in the STO reaction, leading to a higher olefin/paraffin ratio.

New horizon in C1 chemistry: breaking the selectivity limitation in transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels

Recent advances in bifunctional catalysis for conversion of syngas and hydrogenation of CO₂ into chemicals and fuels have been highlighted.

Synthesis of lower olefins from syngas over Zn/Al2O3–SAPO-34 hybrid catalysts: role of doped Zr and influence of the Zn/Al2O3ratio

Hybrid catalysts composed of different loadings of Zr-promoted Zn/Al₂O₃with SAPO-34 zeolite were investigated for the direct synthesis of lower olefins from syngas in a fixed-bed reactor.