Highly Efficient and Stable Methane Dry Reforming Enabled by a Single-Site Cationic Ni Catalyst.

Zeolite-supported nickel (Ni) catalysts have been extensively studied for the dry reforming of methane (DRM). It is generally believed that prior to or during the reaction, Ni is reduced to a metallic state to act as the catalytic site. Here, we employed a ligand-protected synthesis method to achieve a high degree of Ni incorporation into the framework of the MFI zeolite. The incorporated Ni species retained their cationic nature during the DRM reaction carried out at 600 °C, exhibiting higher apparent catalytic activity and significantly greater catalytic stability in comparison to supported metallic Ni particles at the same loading. From theoretical and experimental evidence, we conclude that the incorporation of Ni into the zeolite framework leads to the formation of metal-oxygen (Niδ+-O(2-ξ)-) pairs, which serve as catalytic active sites, promoting the dissociation of C-H bonds in CH4 through a mechanism distinct from that of metallic Ni. The conversion of CH4 on cationic Ni single sites follows the CHx oxidation pathway, which is characterized by the rapid transformation of partial cracking intermediates CHx*, effectively inhibiting coke formation. The presence of the CHx oxidation pathway was experimentally validated by identifying the reaction intermediates. These new mechanistic insights elucidate the exceptional performance of the developed Ni-MFI catalyst and offer guidance for designing more efficient and stable Ni-based DRM catalysts.

Zeolite Synthesis in the Presence of Metallosiloxanes for the Quantitative Encapsulation of Metal Species for the Selective Catalytic Reduction (SCR) of NOx.

Metal encapsulation in zeolitic materials through one-pot hydrothermal synthesis (HTS) is an attractive technique to prepare zeolites with a high metal dispersion. Due to its simplicity and the excellent catalytic performance observed for several catalytic systems, this method has gained a great deal of attention over the last few years. While most studies apply synthetic methods involving different organic ligands to stabilize the metal under synthesis conditions, here we report the use of metallosiloxanes as an alternative metal precursor. Metallosiloxanes can be synthesized from simple and cost-affordable chemicals and, when used in combination with zeolite building blocks under standard synthesis conditions, lead to quantitative metal loading and high dispersion. Thanks to the structural analogy of siloxane with TEOS, the synthesis gel stabilizes by forming siloxane bridges that prevent metal precipitation and clustering. When focusing on Fe-encapsulation, we demonstrate that Fe-MFI zeolites obtained by this method exhibit high catalytic activity in the NH3 -mediated selective catalytic reduction (SCR) of NOx along with a good H2 O/SO2 tolerance. This synthetic approach opens a new synthetic route for the encapsulation of transition metals within zeolite structures.

Modifying the Hydrogenation Activity of Zeolite Beta for Enhancing the Yield and Selectivity for Fuel-Range Alkanes from Carbon Dioxide.

In order to empower a circular carbon economy for addressing global CO2 emissions, the production of carbon-neutral fuels is especially desired, since addressing the global fuel demand via this route has the potential to significantly mitigate carbon emissions. In this study, we report a multifunctional catalyst combination consisting of a potassium promoted iron catalyst (Fe-K) and platinum containing zeolite beta (Pt-beta) which produces an almost entirely paraffinic mixture (up to C10 hydrocarbons) via CO2 hydrogenation in one step. Here, the Fe catalyst is responsible for modified Fischer-Tropsch synthesis from CO2 while Pt-beta is instrumental in tuning the product distribution almost entirely towards paraffins (both linear and branched) presumably via a combination of cracking and hydrogenation. The optimal temperature of operation was estimated to be 325 °C for the production of higher paraffins (C5 -C10 ) with a selectivity of ca. 28 % at a CO2 conversion of ca. 31 %.

Fundamentals and applications of photo-thermal catalysis.

Correction for 'Fundamentals and applications of photo-thermal catalysis' by Diego Mateo et al., Chem. Soc. Rev., 2021, 50, 2173-2210, DOI: 10.1039/D0CS00357C.

Designing a Multifunctional Catalyst for the Direct Production of Gasoline-Range Isoparaffins from CO2.

The production of carbon-neutral fuels from CO2 presents an avenue for causing an appreciable effect in terms of volume toward the mitigation of global carbon emissions. To that end, the production of isoparaffin-rich fuels is highly desirable. Here, we demonstrate the potential of a multifunctional catalyst combination, consisting of a methanol producer (InCo) and a Zn-modified zeolite beta, which produces a mostly isoparaffinic hydrocarbon mixture from CO2 (up to ∼85% isoparaffin selectivity among hydrocarbons) at a CO2 conversion of >15%. The catalyst combination was thoroughly characterized via an extensive complement of techniques. Specifically, operando X-ray absorption spectroscopy (XAS) reveals that Zn (which plays a crucial role of providing a hydrogenating function, improving the stability of the overall catalyst combination and isomerization performance) is likely present in the form of Zn6O6 clusters within the zeolite component, in contrast to previously reported estimations.

Fundamentals and applications of photo-thermal catalysis.

Photo-thermal catalysis has recently emerged as an alternative route to drive chemical reactions using light as an energy source. Through the synergistic combination of photo- and thermo-chemical contributions of sunlight, photo-thermal catalysis has the potential to enhance reaction rates and to change selectivity patterns, even under moderate operation conditions. This review provides the fundamentals of localized surface plasmon resonance (LSPR) that explain the photo-thermal effect in plasmonic structures, describes the different mechanistic pathways underlying photo-thermal catalysis, suggests methodologies to disentangle the reaction mechanisms and proposes material design strategies to improve photo-thermal performance. Ultimately, the goal is to pave the way for the wide implementation of this promising technology in the production of synthetic fuels and chemicals.