Oscillatory behaviour of catalytic properties, structure and temperature during the catalytic partial oxidation of methane on Pd/Al(2)O(3)

Oscillatory Active State of a Pd Nanocatalyst Identified by In Situ Capture of the Instantaneous Structure-Activity Change at the Atomic Scale

Identifying the active phase with the highest activity, which is long-believed to be a steady state of the catalyst, is the basis of rational design of heterogeneous catalysis. In this work, we performed detailed in situ investigations, successfully capturing the instantaneous structure-activity change in oscillating Pd nanocatalysts during methane oxidation, which reveals an unprecedented oscillatory active state. Combining in situ quantitative environmental transmission electron microscopy and highly sensitive online mass spectrometry, we identified two distinct phases for the reaction: one where the Pd nanoparticles refill with oxygen, and the other, a period of abrupt pumping of oxygen and boosted methane oxidation within about 1 s. It is the rapid reduction process that shows the highest activity for total oxidation of methane, not a PdO or Pd steady state under the conditions applied here (methane:oxygen = 5:1). This observation challenges the traditional understanding of the active phase and requires a completely different strategy for catalyst optimization.

Infrared Thermography as an Operando Tool for the Analysis of Catalytic Processes: How to Use it?

Infrared (IR) thermography is a powerful tool to measure temperature with high space and time resolution. A particularly interesting application of this technology is in the field of catalysis, where the method can provide new insights into dynamic surface reactions. This paper presents guidelines for the development of a reactor cell that can aid in the efficient exploitation of infrared thermography for the investigation of catalytic and other surface reactions. Firstly, the necessary properties of the catalytic reactor are described. Secondly, we analyze the requirements towards the catalytic system to be directly observable by IR thermography. This includes the need for a catalyst that provides a sufficiently high heat production (or absorption) rate. To achieve true operando investigation conditions, some dedicated equipment must be developed. Here, we provide the guidelines to assemble a chemical reactor with an IR transmitting window through which the reaction can be studied with the infrared camera along with other best practice tips to achieve results. Furthermore, we present selected examples of catalytic reactions that can be monitored by IR thermography, showing the potential of the technology in revealing transient and steady state chemical phenomena.

Infrared Thermography as a Powerful, Versatile, and Elegant Research Tool in Chemistry: Principles and Application to Catalysis and Adsorption

In this Review, diverse chemical problems that have been approached by means of infrared thermography (IRT) are covered in depth. Moreover, some novel steps forward in this field are made, described and discussed. Namely, the latest-generation IRT performance capabilities are harnessed in full; the initial phase of catalytic CO oxidation (called "fast ignition") is presented at the 0.01 s temporal resolution; at the same resolution, the thermal manifestation of the adsorption-desorption wave propagation after the gaseous reactant pulsed (0.6 s) wetting is exhibited. Furthermore, a radical difference in the thermal behavior of differently calcined γ-Al₂ O₃ supported Au catalysts, which underwent successive H₂ O and CO attacks, is demonstrated, and the generally accepted fact that the catalyst temperature reflects the catalytic activity is validated experimentally. It is shown that latest-generation IRT may serve as unique and highly informative research tool in chemistry.

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

In the future, (electro-)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power-to-chemical processes require a shift from steady-state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well-known that the structure of catalysts is very dynamic. However, in-depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time-resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions.

Photoinduced oxygen prompted iron–iron oxide catalyzed clock reaction: a mimic of the blue bottle experiment

Mixed-valent iron–iron oxide nanoparticles were synthesized and fully characterized using PXRD, SEM, TEM, EDX, XPS and subsequently used for clock reaction of organic dyes.

Pt–CeO2 nanoporous spheres – an excellent catalyst for partial oxidation of methane: effect of the bimodal pore structure

Bimodal pore size distribution played the most important role for the catalyst's superior activity during POM.

Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques

We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

Infrared thermography as a high-throughput tool in catalysis research

The so-called "emissivity corrected infrared thermography" (ecIRT) has been successfully developed and used to great effect in the field of combinatorial high-throughput studies in catalysis. A short introduction to the basics of ecIRT and the description of a typical setup is given. Research efforts from 1998 until present are summarized and selected publications with IRT applications in catalysis are highlighted. The last section of the article covers potential problems, which the observant may misinterpret as activity of the materials. The effects are classified and it is explained why they occur and what can be done to bypass them.

Hard and soft X-ray microscopy and tomography in catalysis: bridging the different time and length scales

X-ray microscopic techniques are excellent and presently emerging techniques for chemical imaging of heterogeneous catalysts. Spatially resolved studies in heterogeneous catalysis require the understanding of both the macro and the microstructure, since both have decisive influence on the final performance of the industrially applied catalysts. A particularly important aspect is the study of the catalysts during their preparation, activation and under operating conditions, where X-rays have an inherent advantage due to their good penetration length especially in the hard X-ray regime. Whereas reaction cell design for hard X-rays is straightforward, recently smart in situ cells have also been reported for the soft X-ray regime. In the first part of the tutorial review, the constraints from a catalysis view are outlined, then the scanning and full-field X-ray microscopy as well as coherent X-ray diffraction imaging techniques are described together with the challenging design of suitable environmental cells. Selected examples demonstrate the application of X-ray microscopy and tomography to monitor structural gradients in catalytic reactors and catalyst preparation with micrometre resolution but also the possibility to follow structural changes in the sub-100 nm regime. Moreover, the potential of the new synchrotron radiation sources with higher brilliance, recent milestones in focusing of hard X-rays as well as spatiotemporal studies are highlighted. The tutorial review concludes with a view on future developments in the field of X-ray microscopy that will have strong impact on the understanding of catalysts in the future and should be combined with in situ electron microscopic studies on the nanoscale and other spectroscopic studies like microRaman, microIR and microUV-vis on the macroscale.