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In the last few decades, massive effort has been expended in heterogeneous catalysis to develop new materials presenting high conversion, selectivity, and stability even under high-temperature and high-pressure conditions. In this context, CO 2 hydrogenation is an interesting reaction where the catalyst local structure is strongly related to the development of an active and stable material under hydrothermal conditions at T / P > 300 °C/30 bar. In order to clarify the relationship between catalyst local ordering and its activity/stability, we herein report a combined laboratory and synchrotron investigation of aliovalent element (Ce/Zn/Ga)-containing ZrO 2 matrixes. The results reveal the influence of similar average structures with different short-range orderings on the catalyst properties. Moreover, a further step toward the comprehension of the oxygen vacancy formation mechanism in Ce- and Ga-ZrO 2 catalysts is reported. Finally, the reported results illustrate a robust method to guide local structure determination and ultimately help to avoid overuse of the "solid solution" definition.

Copper single-site catalysts supported on Zr-based metal-organic frameworks (MOFs) are well-known systems in which the nature of the active sites has been deeply investigated. Conversely, the redox chemistry of the Ce-counterparts is more limited, because of the often-unclear Cu 2+ /Cu + and Ce 4+ /Ce 3+ pairs behavior. Herein, we studied a novel Cu 2+ single-site catalyst supported on a defective Ce-MOF, Cu/UiO-67(Ce), as a catalyst for the CO oxidation reaction. Based on a combination of in situ DRIFT and operando XAS spectroscopies, we established that Cu + sites generated during catalysis play a pivotal role. Moreover, the oxygen vacancies associated with Ce 3+ sites and presented in the defective Cu/UiO-67(Ce) material are able to activate the O 2 molecules, closing the catalytic cycle. The results presented in this work open a new route for the design of active and stable single-site catalysts supported on defective Ce-MOFs.

ZnO-ZrO 2 mixed oxide (ZnZrO x ) catalysts are widely studied as selective catalysts for CO 2 hydrogenation into methanol at high-temperature conditions (300-350 °C) that are preferred for the subsequent in situ zeolite-catalyzed conversion of methanol into hydrocarbons in a tandem process. Zn, a key ingredient of these mixed oxide catalysts, is known to volatilize from ZnO under high-temperature conditions, but little is known about Zn mobility and volatility in mixed oxides. Here, an array of ex situ and in situ characterization techniques (scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Infrared (IR)) was used to reveal that Zn 2+ species are mobile between the solid solution phase with ZrO 2 and segregated and/or embedded ZnO clusters. Upon reductive heat treatments, partially reversible ZnO cluster growth was observed above 250 °C and eventual Zn evaporation above 550 °C. Extensive Zn evaporation leads to catalyst deactivation and methanol selectivity decline in CO 2 hydrogenation. These findings extend the fundamental knowledge of Zn-containing mixed oxide catalysts and are highly relevant for the CO 2 -to-hydrocarbon process optimization., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The interaction between metal particles and the oxide support, the so-called metal-support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure-performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO 2 (Co/TiO 2 ) is an industrially relevant catalyst applied in Fischer-Tropsch synthesis. Although it is widely acknowledged that Co/TiO 2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material's surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH 4 -modified TiO 2 under H 2 , O 2 , and CO 2 :H 2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study's unique features. It is shown that under H 2 , cobalt particles are encapsulated below a stoichiometric TiO 2 layer. This arrangement is preserved under CO 2 hydrogenation conditions (i.e., CO 2 :H 2 ), but changes rapidly upon exposure to O 2 . The pretreatment of the TiO 2 support with NaBH 4 affects the surface mobility and prevents TiO 2 spillover onto Co particles.

In this work, we have synthesized through an efficient electrostatic deposition a Pt single-atom catalyst (SAC) supported on a Ce-MOF. The basic solution employed in the impregnation process favors the deprotonation of the hydroxyl groups allocated on the clusters that can easily interact with the cationic Pt species. The resulting material, denoted as Pt/UiO-66(Ce), shows an increment of Ce 3+ content, as demonstrated by UV-vis and Ce L 3 -edge XANES spectroscopy. These Ce 3+ species and their corresponding oxygen vacancies are able to accommodate very disperse Pt single sites. Moreover, Pt L 3 -edge XANES and CO-FTIR spectroscopy confirm the cationic nature of the supported Pt δ+ (2+ < δ < 4+). For comparison purpose, we have synthesized and characterized a well-known Pt single-site catalyst supported on nanocrystalline ceria, denoted as Pt/ n CeO 2 . Since the simultaneous presence of Ce 3+ and Pt δ+ on the MOF clusters were able to activate the oxygen molecules and the CO molecule, respectively, we tested Pt/UiO-66(Ce) for the CO oxidation reaction. Interestingly, this catalyst showed ∼six-fold increment in activity in comparison with the traditional Pt/ n CeO 2 material. Finally, the characterization after catalysis reveals that the Pt nature is preserved and that the activity is maintained during 14 h at 100 °C without any evidence of deactivation., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

CO 2 hydrogenation to methane is gaining increasing interest as one of the most promising ways to store intermittent renewable energy in the form of chemical fuels. Ni particles supported on CeO 2 represent a highly efficient, stable and inexpensive catalyst for this reaction. Herein, Ni-doped CeO 2 nanoparticles were tested for CO 2 methanation showing an extremely high Ni mass-specific activity and CH 4 selectivity. Operando characterization reveals that this performance is tightly associated with ionic Νi and Ce 3+ surface sites, while formation of metallic Ni does not seem to considerably promote the reaction. Theoretical calculations confirmed the stability of interstitial ionic Ni sites on ceria surfaces and highlighted the role of Ce-O frustrated Lewis pair (FLP), Ni-O classical Lewis pair (CLP) and Ni-Ce pair sites to the activation of H 2 and CO 2 molecules. To a large extent, the theoretical predictions were validated by in situ spectroscopy under H 2 and CO 2  : H 2 gaseous environments., (© 2023 Wiley-VCH GmbH.)

Frustrated Lewis pairs (FLPs), discovered in the last few decades for homogeneous catalysts and in the last few years also for heterogeneous catalysts, are stimulating the scientific community's interest for their potential in small-molecule activation. Nevertheless, how an FLP activates stable molecules such as CO 2 is still undefined. Through a careful spectroscopic study, we here report the formation of FLPs over a highly defective CeO 2 sample prepared by microwave-assisted synthesis. Carbon dioxide activation over FLP is shown to occur through a bidentate carbonate bridging the FLP and implying a Ce 3+ -to-CO 2 charge transfer, thus enhancing its activation. Carbon dioxide reaction with methanol to form monomethylcarbonate is here employed to demonstrate active roles of FLP and, eventually, to propose a reaction mechanism clarifying the role of Ce 3+ and oxygen vacancies.

The reaction mechanism of dimethyl carbonate (DMC) production over ZrO 2 from CO 2 and CH 3 OH is well-known, but the level of understanding has not improved in the last decade. Most commonly, the reaction mechanism has been explored in the gas phase, whilst DMC production occurs in the liquid phase. To overcome this contradiction, we exploited in situ ATR-IR spectroscopy to study DMC formation over ZrO 2 in the liquid phase. A multiple curve resolution-alternate least square (MCR-ALS) approach was applied to spectra collected during the CO 2 /CH 3 OH interaction with the catalyst surface, leading to the identification of five pure components with their respective concentration profiles. CO 2 and CH 3 OH activation to carbonates and methoxide species was found to strongly depend on the reaction temperature. Low temperature prevents methanol dissociation leaving a catalyst covered with stable carbonates, whilst higher temperature decreases the stability of the carbonates and enhances the formation of methoxides. A reaction path involving the methoxide/carbonate interaction at the surface was observed at low temperature (≤50 °C). We propose that a different reaction path, independent of carbonate formation and involving the direct CO 2 /methoxide interplay, occurs at 70 °C.

The valorization of CO 2 to produce high-value chemicals, such as methanol and hydrocarbons, represents key technology in the future net-zero society. Herein, we report further investigation of a PdZn/ZrO 2 + SAPO-34 catalyst for conversion of CO 2 and H 2 into propane, already presented in a previous work. The focus of this contribution is on the scale up of this catalyst. In particular, we explored the effect of mixing (1:1 mass ratio) and shaping the two catalyst functions into tablets and extrudates using an alumina binder. Their catalytic performance was correlated with structural and spectroscopic characteristics using methods such as FT-IR and X-ray absorption spectroscopy. The two scaled-up bifunctional catalysts demonstrated worse performance than a 1:1 mass physical mixture of the two individual components. Indeed, we demonstrated that the preparation negatively affects the element distribution. The physical mixture is featured by the presence of a PdZn alloy, as demonstrated by our previous work on this sample and high hydrocarbon selectivity among products. For both tablets and extrudates, the characterization showed Zn migration to produce Zn aluminates from the alumina binder phase upon reduction. Moreover, the extrudates showed a remarkable higher amount of Zn aluminates before the activation rather than the tablets. Comparing tablets and extrudates with the physical mixture, no PdZn alloy was observed after activation and only the extrudates showed the presence of metallic Pd. Due to the Zn migration, SAPO-34 poisoning and subsequent deactivation of the catalyst could not be excluded. These findings corroborated the catalytic results: Zn aluminate formation and Pd 0 separation could be responsible for the decrease of the catalytic activity of the extrudates, featured by high methane selectivity and unconverted methanol, while tablets displayed reduced methanol conversion to hydrocarbons mainly attributed to the partial deactivation of the SAPO-34.

The development of Ce-based materials is directly dependent on the catalyst surface defects, which is caused by the calcination steps required to increase structural stability. At the same time, the evaluation of cerium's redox properties under reaction conditions is of increasing relevant importance. The synthesis of Ce-UiO-66 and CeZr-UiO-66 and their subsequent calcination are presented here as a simple and inexpensive approach for achieving homogeneous and stable CeO 2 and CeZrO x nanocrystals. The resulting materials constitute an ideal case study to thoroughly understand cerium redox properties. The Ce 3+ /Ce 4+ redox properties are investigated by H 2 -TPR experiments exploited by in situ FT-IR and Ce M 5 -edge AP-NEXAFS spectroscopy. In the latter case, Ce 3+ formation is quantified using the MCR-ALS protocol. FT-IR is then presented as a high potential/easily accessible technique for extracting valuable information about the cerium oxidation state under operating conditions. The dependence of the OH stretching vibration frequency on temperature and Ce reduction is described, providing a novel tool for qualitative monitoring of surface oxygen vacancy formation. Based on the reported results, the molecular absorption coefficient of the Ce 3+ characteristic IR transition is tentatively evaluated, thus providing a basis for future Ce 3+ quantification through FT-IR spectroscopy. Finally, the FT-IR limitations for Ce 3+ quantification are discussed.

Background: Evidence among key populations supports acceptability of HIV self-testing (HIVST) due to its privacy and convenience. However, insufficient research has been done among transgender women (TGW), especially in Latin America. Consequently, the aim of this study was to explore the acceptability, perceptions and recommendations for HIVST implementation among TGW in Buenos Aires., Methods: A focus group was conducted in July 2019. Particpants were invited to touch and learn about a displayed HIVST kit. The following main topics were explored: acceptability, reasons for seeking self-testing, preferences for training, distribution, periodicity and recommendations for HIVST implementation., Results: The sample consisted of 12 TGWs; mean age of 26 years (IQR = 22-28); 66% had history of sex-work. The main motivations for seeking HIVST were convenience, privacy, and usage to reduce stigma and discrimination by health-care providers. Recommendations for HIVST were: distribution from primary health centers and trans-sensitive centers; affordable price; assistance by peer health promoters; and the provision of clear written and video instructions., Conclusions: Tailored implementation of HIVST can increase HIV testing rates, early detection, and linkage to HIV-care in this high-prevalence group. This study provided community-driven suggestions to inform and adapt an HIVST feasibility pilot study and future implementation in Argentina.

The production of carbon-rich hydrocarbons via CO 2 valorization is essential for the transition to renewable, non-fossil-fuel-based energy sources. However, most of the recent works in the state of the art are devoted to the formation of olefins and aromatics, ignoring the rest of the hydrocarbon commodities that, like propane, are essential to our economy. Hence, in this work, we have developed a highly active and selective PdZn/ZrO 2 +SAPO-34 multifunctional catalyst for the direct conversion of CO 2 to propane. Our multifunctional system displays a total selectivity to propane higher than 50% (with 20% CO, 6% C 1 , 13% C 2 , 10% C 4 , and 1% C 5 ) and a CO 2 conversion close to 40% at 350 °C, 50 bar, and 1500 mL g -1 h -1 . We attribute these results to the synergy between the intimately mixed PdZn/ZrO 2 and SAPO-34 components that shifts the overall reaction equilibrium, boosting CO 2 conversion and minimizing CO selectivity. Comparison to a PdZn/ZrO 2 +ZSM-5 system showed that propane selectivity is further boosted by the topology of SAPO-34. The presence of Pd in the catalyst drives paraffin production via hydrogenation, with more than 99.9% of the products being saturated hydrocarbons, offering very important advantages for the purification of the products., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)