Emergence of chaos in a compartmentalized catalytic reaction nanosystem.

In compartmentalized systems, chemical reactions may proceed in differing ways even in adjacent compartments. In compartmentalized nanosystems, the reaction behaviour may deviate from that observed on the macro- or mesoscale. In situ studies of processes in such nanosystems meet severe experimental challenges, often leaving the field to theoretical simulations. Here, a rhodium nanocrystal surface consisting of different nm-sized nanofacets is used as a model of a compartmentalized reaction nanosystem. Using field emission microscopy, different reaction modes are observed, including a transition to spatio-temporal chaos. The transitions between different modes are caused by variations of the hydrogen pressure modifying the strength of diffusive coupling between individual nanofacets. Microkinetic simulations, performed for a network of 52 coupled oscillators, reveal the origins of the different reaction modes. Since diffusive coupling is characteristic for many living and non-living compartmentalized systems, the current findings may be relevant for a wide class of reaction systems.

Lanthanum modulated reaction pacemakers on a single catalytic nanoparticle.

Promoters are important in catalysis, but the atomistic details of their function and particularly their role in reaction instabilities such as kinetic phase transitions and oscillations are often unknown. Employing hydrogen oxidation as probe reaction, a Rh nanotip for mimicking a single Rh nanoparticle and field electron microscopy for in situ monitoring, we demonstrate a La-mediated local catalytic effect. The oscillatory mode of the reaction provides a tool for studying the interplay between different types of reaction pacemakers, i.e., specific local surface atomic configurations that initiate kinetic transitions. The presence of La shifts the bistable reaction states, changes the oscillation pattern and deactivates one of two pacemaker types for the La-free surface. The observed effects originate from the La-enhanced oxygen activation on the catalyst. The experimental observations are corroborated by micro-kinetic model simulations comprising a system of 25 coupled oscillators.

Imaging Interface and Particle Size Effects by In Situ Correlative Microscopy of a Catalytic Reaction.

The catalytic behavior of Rh particles supported by three different materials (Rh, Au, and ZrO2) in H2 oxidation has been studied in situ by correlative photoemission electron microscopy (PEEM) and scanning photoemission electron microscopy (SPEM). Kinetic transitions between the inactive and active steady states were monitored, and self-sustaining oscillations on supported Rh particles were observed. Catalytic performance differed depending on the support and Rh particle size. Oscillations varied from particle size-independent (Rh/Rh) via size-dependent (Rh/ZrO2) to fully inhibited (Rh/Au). For Rh/Au, the formation of a surface alloy induced such effects, whereas for Rh/ZrO2, the formation of substoichiometric Zr oxides on the Rh surface, enhanced oxygen bonding, Rh-oxidation, and hydrogen spillover onto the ZrO2 support were held responsible. The experimental observations were complemented by micro-kinetic simulations, based on variations of hydrogen adsorption and oxygen binding. The results demonstrate how correlative in situ surface microscopy enables linking of the local structure, composition, and catalytic performance.

Reaction Modes on a Single Catalytic Particle: Nanoscale Imaging and Micro-Kinetic Modeling.

The kinetic behavior of individual Rh(hkl) nanofacets coupled in a common reaction system was studied using the apex of a curved rhodium microcrystal (radius of 0.65 µm) as a model of a single catalytic particle and field electron microscopy for in situ imaging of catalytic hydrogen oxidation. Depending on the extent of interfacet coupling via hydrogen diffusion, different oscillating reaction modes were observed including highly unusual multifrequential oscillations: differently oriented nanofacets oscillated with differing frequencies despite their immediate neighborhood. The transitions between different modes were induced by variations in the particle temperature, causing local surface reconstructions, which create locally protruding atomic rows. These atomic rows modified the coupling strength between individual nanofacets and caused the transitions between different oscillating modes. Effects such as entrainment, frequency locking, and reconstruction-induced collapse of spatial coupling were observed. To reveal the origin of the different experimentally observed effects, microkinetic simulations were performed for a network of 105 coupled oscillators, modeling the individual nanofacets communicating via hydrogen surface diffusion. The calculated behavior of the oscillators, the local frequencies, and the varying degree of spatial synchronization describe the experimental observations well.

Pattern Formation in Catalytic H2 Oxidation on Rh: Zooming in by Correlative Microscopy.

Spatio-temporal nonuniformities in H2 oxidation on individual Rh(h k l) domains of a polycrystalline Rh foil were studied in the 10-6 mbar pressure range by photoemission electron microscopy (PEEM), X-ray photoemission electron microscopy (XPEEM), and low-energy electron microscopy (LEEM). The latter two were used for in situ correlative microscopy to zoom in with significantly higher lateral resolution, allowing detection of an unusual island-mediated oxygen front propagation during kinetic transitions. The origin of the island-mediated front propagation was rationalized by model calculations based on a hybrid approach of microkinetic modeling and Monte Carlo simulations.

Single-Particle Catalysis: Revealing Intraparticle Pacemakers in Catalytic H2 Oxidation on Rh.

Self-sustained oscillations in H2 oxidation on a Rh nanotip mimicking a single catalytic nanoparticle were studied by in situ field emission microscopy (FEM). The observed spatio-temporal oscillations result from the coupling of subsurface oxide formation/depletion with reaction front propagation. An original sophisticated method for tracking kinetic transition points allowed the identification of local pacemakers, initiating kinetic transitions and the nucleation of reaction fronts, with much higher temporal resolution than conventional processing of FEM video files provides. The pacemakers turned out to be specific surface atomic configurations at the border between strongly corrugated Rh{973} regions and adjacent relatively flat terraces. These structural ensembles are crucial for reactivity: while the corrugated region allows sufficient oxygen incorporation under the Rh surface, the flat terrace provides sufficient hydrogen supply required for the kinetic transition, highlighting the importance of interfacet communication. The experimental observations are complemented by mean-field microkinetic modeling. The insights into the initiation and propagation of kinetic transitions on a single catalytic nanoparticle demonstrate how in situ monitoring of an ongoing reaction on individual nanofacets can single out active configurations, especially when combined with atomically resolving the nanoparticle surface by field ion microscopy (FIM).

A novel wireless sample temperature control system for field ion, field electron, and atom probe techniques.

A novel sample temperature control system for field ion microscopy (FIM), field electron microscopy (FEM), and atom probe techniques based on wireless data transmission was designed, built, and applied for FIM and FEM studies of surface reactions. The system solves the longstanding problem of the temperature control of micrometer- to nanometer-sized samples during the operation in field emission based techniques. The new system can also be used for other applications requiring the specimen to be under high electric potential (tens of kilovolts or even higher). The chosen case studies of nanocatalysis demonstrate the capabilities and superior performance of the new temperature control system.

Thyroid metastases of renal cell carcinoma: clinical course in 45 patients undergoing surgery. Assessment of factors affecting patients' survival.

BACKGROUND: Metastases of renal cell carcinoma (RCC) to the thyroid gland are uncommon. There is no clear consensus regarding the role of surgery in metastatic disease to the thyroid since most clinical studies include small numbers of patients. Also, risk factors associated with disease progression following thyroidectomy are not yet defined. We examined the determinants of the outcome in patients undergoing surgery for thyroid metastases of RCC. METHODS: The medical records of 45 patients undergoing resection of thyroid metastases of RCC at 15 institutions in Germany and Austria were reviewed retrospectively. The outcome parameters assessed were overall survival and tumor-related survival. Factors associated with disease progression following thyroid surgery have been calculated. RESULTS: The overall 5-year survival rate following thyroid metastasectomy was 51%. Nineteen patients died during the study: 14 of disseminated disease and 5 of non-tumor-related causes. In the multivariate analysis, the prognosis was significantly worse in patients older than > or = 70 years and in patients who had undergone nephrectomy for metastases in the contralateral kidney during the course of the disease. Nine patients developed a thyroid recurrence following surgery. No local disease relapse occurred if resection margins were documented to be free of the tumor. Of the 45 patients with thyroid metastases, 14 (31%) developed pancreatic metastases during the course of disease. Ten of these patients also underwent pancreatic surgery with a 5-year survival rate of 43% in this subgroup. CONCLUSIONS: The overall survival of patients undergoing thyroidectomy for metastases of RCC is affected rather by general health status than by tumor-related factors. There is a significant coincidence of thyroid and pancreatic metastases of RCC.

Renal cell carcinoma metastases to the thyroid gland-8 cases reported.

OBJECTIVE: Clinically important, isolated metastases to the thyroid gland is a rare occurrence. Renal cell carcinoma (RCC) is the most common primary tumor site. We report on 8 cases of late onset metachronous thyroid metastases of RCC. DESIGN: Eight patients presented with metachronous thyroid metastases at a median of 12 years (range 9-18 years) after nephrectomy for RCC. Two patients had simultaneous lung and lymph node metastases, respectively. Four patients had been previously operated for other metastases 1 to 5 years earlier, three of them due to pancreatic metastases. The leading symptom was neck enlargement in all but one case. MAIN OUTCOME: Four total thyroidectomies, 3 subtotal resections, and 1 lobectomy were performed. Complete removal of metastases were achieved in all but one case. There was no postoperative morbidity. Six metastases were bilateral, two unilateral. The 4 year overall survival rate following metastasectomy was 53%, median survival from the date of nephrectomy was 21 years. CONCLUSION: Long-term survival can be achieved after resection of isolated metachronous RCC metastases to the thyroid gland. Total thyroidectomy is not required, unless it is necessary for complete metastasectomy.