Combined high‐resolution fluorescence detection X‐ray absorption near‐edge spectroscopy, X‐ray diffraction, and X‐ray emission spectroscopy have been employed under operando conditions to obtain detailed new insight into the nature of the Mo species on zeolite ZSM‐5 during methane dehydroaromatization. The results show that isolated Mo–oxo species present after calcination are converted by CH4 into metastable MoCxOy species, which are primarily responsible for C2Hx/C3Hx formation. Further carburization leads to MoC3 clusters, whose presence coincides with benzene formation. Both sintering of MoC3 and accumulation of large hydrocarbons on the external surface, evidenced by fluorescence‐lifetime imaging microscopy, are principally responsible for the decrease in catalytic performance. These results show the importance of controlling Mo speciation to achieve the desired product formation, which has important implications for realizing the impact of CH4 as a source for platform chemicals.

Copper-exchanged zeolite chabazite (Cu-SSZ-13) was recently commercialized for the selective catalytic reduction of NOX with ammonia in vehicle emissions as it exhibits superior reaction performance and stability compared to all other catalysts, notably Cu-ZSM-5. Herein, the 3D distributions of Cu as well as framework elements (Al, O, Si) in both fresh and aged Cu-SSZ-13 and Cu-ZSM-5 are determined with nanometer resolution using atom probe tomography (APT), and correlated with catalytic activity and other characterizations. Both fresh catalysts contain a heterogeneous Cu distribution, which is only identified due to the single atom sensitivity of APT. After the industry standard 135,000 mile simulation, Cu-SSZ-13 shows Cu and Al clustering, whereas Cu-ZSM-5 is characterized by severe Cu and Al aggregation into a copper aluminate phase (CuAl2O4 spinel). The application of APT as a sensitive and local characterization method provides identification of nanometer scale heterogeneities that lead to catalytic activity and material deactivation.

The direct conversion of methane into methanol is considered as one of the holy grails in hydrocarbon chemistry and recently it was found that small pore zeolites, such as Cu-SSZ-13, Cu-SSZ-16 and Cu-SSZ-39, are active for this process. Here, we propose a reaction mechanism based on spectroscopic evidence for the methane-to-methanol reaction over Cu- . Using in situ FT-IR and operando UVvis-NIR DRS, performed on a series of different Cu-ion-exchanged SSZ-13 zeolites, both a mono-nuclear site or a dimeric copper active site are consistent with the observations of this study. These proposed active site(s) are characterized by a ν OH at ∼3654 cm −1 and a charge transfer (CT) transition at ∼29 000 cm −1 .We have further evidence to complete the full catalytic cycle to methanol, including the formation of the reaction intermediate CuIJCH 3 )IJH 2 O), which is characterized by overtone transitions, i.e., a 2ν CH at ∼4200 cm −1 and a 2ν OH at ∼5248 cm −1 . We found that increasing the pre-oxidation temperature from 450°C to 550°C resulted in a 15% increase in methanol production, as well as a concomitant increase of the 29 000 cm −1 CT transition. Furthermore, Cu-exchanged SSZ-13 zeolites, which perform well in the NH 3 -SCR reaction at 200°C (the low temperature regime), also show a high activity in the methane-to-methanol reaction and vice versa, leading us to believe that this material has a similar if not the same active site for both the catalytic reduction of NO and the stepwise reaction towards methanol.

Zeolite-based catalyst bodies are commonly employed in a range of important industrial processes. Depending on the binder and shaping method chosen, vast differences in the reactivity, selectivity and stability are obtained. Here, three highly complementary micro-spectroscopic techniques were employed to study zeolite ZSM-5-binder interactions in SiO2-, Al2O3-, SiO2 : Al2O3- (2 : 1 mix) and kaolinite-bound catalyst pellets. We establish how their preparation influences the zeolite-clay/binder interactions. Using thiophene as an acid-catalyzed staining reaction, light absorbing oligomers produced in each sample were followed. To our surprise, kaolinite decreased the overall reactivity of the sample due to the phase change of the binder, creating a hard impenetrable outer layer. Aluminum migration to the zeolite was observed when Al2O3 was selected as a binder, creating additional Brønsted acid sites, which favored the formation of ring-opened thiophene oligomers compared to the larger oligomer species produced when SiO2 was used as a binder. In the latter case, the interaction of the Si-OH groups in the binder with thiophene was revealed to have a large impact in creating such large oligomer species. Furthermore, the combination of a SiO2 : Al2O3 mix as a binder enhanced the reactivity, possibly due to the creation of additional Brønsted acid sites between the two binder components during pellet preparation. It is evident that, independent of the shaping method, the intimate contact between the zeolite and binder heavily impacts the reactivity and product selectivity, with the type of binder playing a vital role.

Commercialization of CH 4 valorization processes is currently hampered by the lack of suitable catalysts, which should be active, selective, and stable. CH 4 oxychlorination is one of the promising routes to directly functionalize CH 4 , and lanthanidebased catalysts show great potential for this reaction, although relatively little is known about their functioning. In this work, a set of lanthanide oxychlorides (i.e., LnOCl with Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) and Er-and Yb-based catalysts were synthesized, characterized, and tested. All lanthanide-based catalysts can directly activate CH 4 into chloromethanes, but their catalytic properties differ significantly. EuOCl shows the most promising catalytic activity and selectivity, as very high conversion levels (>30%) and chloromethane selectivity values (>50%) can be reached at moderate reaction temperatures (∼425 °C). Operando Raman spectroscopy revealed that the chlorination of the EuOCl catalyst surface is rate-limiting; hence, increasing the HCl concentration improves the catalytic performance. The CO selectivity could be suppressed from 30 to 15%, while the CH 4 conversion more than doubled from 11 to 24%, solely by increasing the HCl concentration from 10 to 60% at 450 °C. Even though more catalysts reported in this study and in the literature show a negative correlation between the S CO and HCl concentration, this effect was never as substantial as observed for EuOCl. EuOCl has promising properties to bring the oxychlorination one step closer to an economically viable CH 4 valorization process.

Combined high-resolution fluorescence detection X-ray absorption near-edge spectroscopy, X-ray diffraction, and X-ray emission spectroscopyh ave been employed under operando conditions to obtain detailed new insight into the nature of the Mo species on zeoliteZ SM-5 during methane dehydroaromatization. The results showthat isolated Mo-oxo species present after calcination are converted by CH 4 into metastable MoC x O y species,w hich are primarily responsible for C 2 H x /C 3 H x formation. Further carburization leads to MoC 3 clusters,w hose presence coincides with benzene formation. Both sintering of MoC 3 and accumulation of large hydrocarbons on the external surface,e videnced by fluorescencelifetime imaging microscopy, are principally responsible for the decrease in catalytic performance.T hese results show the importance of controlling Mo speciation to achieve the desired product formation, which has important implications for realizing the impact of CH 4 as asource for platform chemicals.The increasing availability of cheap natural gas has attracted growing interest towards direct routes for the conversion of methane into high-value chemicals.[1] Catalytic routes that have been investigated include dehydroaromatization, oxidative coupling,and partial oxidation, but are currently not (yet) economically viable.[2] One of these routes,m ethane dehydroaromatization (MDA), is particularly promising for the direct conversion of CH 4 into aromatic compounds and H 2 using metal-exchanged zeolites such as Mo/H-ZSM-5, since it contains acid sites as well as Mo species possessing dehydrogenation and CÀCc oupling functionalities. [1][2][3] It is generally accepted that CH 4 is activated on the exchanged Mo species, forming C 2 H 4 .S ubsequently,C 2 H 4 reacts on the (remaining) Brønsted acid sites and is converted into aromatic compounds,a lso leading to coke formation by the consecutive reaction of aromatic derivatives with light olefins. [3c,4] Although active species are proposed to originate from either (MoO 2 ) 2+ monomers or (Mo 2 O 5 ) 2+ dimers, [3a,c, 5] there is also adebate as to whether the active sites are oxidic,carbidic (MoC x ), or oxycarbidic (MoC x O y )i nn ature. [3a,d, 4, 6] Recently, combined UV/Vis absorption and Raman spectroscopies and DFT calculations have shown the formation of monomeric species upon calcination, demonstrating that the debate over the active sites is still ongoing. [7] In addition, there is no clear understanding of the catalyst deactivation mode,c onsidered to be the main limitation for the commercialization of the process. [1,2] Herein, we present an operando time-resolved combined X-ray diffraction (XRD) and high energy resolution fluorescence detection (K a -detected) X-ray absorption near-edge spectroscopy (HERFD-XANES) study during the MDA reaction on Mo/H-ZSM-5. Thea dvantage of using these techniques in combination is that local structure information around the Mo ions can be considered alongside changes in long-range order,t hat is,t he zeolite fram...

Mesoporous Cu-SSZ-13 was created by first synthesizing zeolite H-SSZ-13 and subsequently desilicating the material by base leaching using NaOH in different concentrations.

Laboratory-based X-ray absorption spectroscopy (XAS) and especially X-ray absorption near-edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory-based setup for performing operando, quasisimultaneous XANES analysis at multiple K-edges, more specifically, operando XANES of mono-, bi-, and trimetallic CO 2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multielement solid catalysts revealed metal-dependent differences in the reducibility and re-oxidation behavior and their influence on the catalytic performance in CO 2 hydrogenation. The applicability of operando laboratory-based XANES at multiple K-edges paves the way for advanced multielement catalyst characterization complementing detailed studies at synchrotron facilities.