Model based optimization of a statistical simulation model for single diamond grinding

We present a model for simulating normal forces arising during a grinding process in cement for single diamond grinding. Assuming the diamond to have the shape of a pyramid, a very fast calculation of force and removed volume can be achieved. The basic approach is the simulation of the scratch track. Its triangle profile is determined by the shape of the diamond. The approximation of the scratch track is realized by stringing together polyhedra. Their sizes depend on both the actual cutting depth and an error implicitly describing the material brittleness. Each scratch track part can be subdivided into three three-dimensional simplices for a straightforward calculation of the removed volume. Since the scratched mineral subsoil is generally inhomogeneous, the forces at different positions of the workpiece are expected to vary. This heterogeneous nature is considered by sampling from a Gaussian random field. To achieve a realistic outcome the model parameters are adjusted applying model based optimization methods. A noisy Kriging model is chosen as surrogate to approximate the deviation between modelled and observed forces. This deviation is minimized and the results of the modelled forces and the actual forces from conducted experiments are rather similar.     

Morphological and chemical influences on alumina-supported palladium catalysts active for the gas phase hydrogenation of crotonaldehyde

A series of five alumina-supported palladium catalysts have previously been prepared and characterised by a combination of CO chemisorption and infrared spectroscopy. The reactive attributes of these catalysts are examined using the hydrogenation of crotonaldehyde as a test reaction, using a modified infrared gas cell as a batch reactor. Periodic scanning of the infrared spectrum of the gaseous phase present over the Pd/Al(2)O(3) catalysts was used to construct reaction profiles. Four of the catalysts were able to facilitate a 2-stage hydrogenation process (crotonaldehyde → butanal → butanol), whilst one catalyst was totally selective for the first stage hydrogenation process (crotonaldehyde → butanal). Rate coefficients for the first and second stage hydrogenation processes are normalised to the number of surface palladium atoms for the particular catalyst. Correlation of these kinetic parameters as a function of mean particle size indicates the first stage process to be structure insensitive, whilst the second stage hydrogenation is structure sensitive. Chlorine residues associated with the preparative process of one of the catalysts is seen to selectively poison the second stage hydrogenation process for that catalyst. Structure/activity relationships are considered to explain the observed trends.     

Tuning the Surface Chemistry of Pd by Atomic C and H: A Microscopic Picture

Palladium is crucial for industry‐related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near‐surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties. Density functional calculations of the interplay of C and H atoms at various concentrations and sites on suitable Pd NPs have been performed, accompanied by catalysis‐relevant experiments on oxide‐supported bare and C‐modified Pd NPs. It is shown that on a Pd₇₉ NP a subsurface C atom destabilizes nearby atoms H at low coverage. Our experiments confirm that H atoms bind more weakly on C‐containing Pd NPs than on C‐free NPs. Various factors related to the presence of both H and C atoms on a Pd₇₉ surface, which may influence the penetration of H atoms from the surface into the subsurface area, have been investigated. Carbon atoms facilitate the subsurface penetration of atomic H both thermodynamically and kinetically when the surface is densely covered by H atoms. Moreover, subsurface H atoms are also energetically favored, even in the absence of C atoms, when several facets of the NP are covered by H atoms.     

Water Interaction with Iron Oxides

We present a mechanistic study on the interaction of water with a well‐defined model Fe₃O₄(111) surface that was investigated by a combination of direct calorimetric measurements of adsorption energies, infrared vibrational spectroscopy, and calculations bases on density functional theory (DFT). We show that the adsorption energy of water (101 kJ mol⁻¹) is considerably higher than all previously reported values obtained by indirect desorption‐based methods. By employing ¹⁸O‐labeled water molecules and an Fe₃O₄ substrate, we proved that the generally accepted simple model of water dissociation to form two individual OH groups per water molecule is not correct. DFT calculations suggest formation of a dimer, which consists of one water molecule dissociated into two OH groups and another non‐dissociated water molecule creating a thermodynamically very stable dimer‐like complex.     

A kinetic study on the conversion of cis-2-butene with deuterium on a Pd/Fe3O4 model catalyst

The conversion of cis-2-butene with deuterium over a well-defined Pd/Fe(3)O(4) model catalyst was studied by isothermal pulsed molecular beam (MB) experiments under ultra high vacuum conditions. This study focuses on the processes related to dissociative hydrogen adsorption and diffusion into the subsurface of Pd nanoparticles and their influence on the activity and selectivity toward competing cis-trans isomerization and hydrogenation pathways. The reactivity was studied both under steady state conditions and in the transient regime, in which the reaction takes place on a D-saturated catalyst, over a large range of reactant pressures and reaction temperatures. We show that large olefin coverages negatively affect the abundance of D species, as indicated by a reduction of both reaction rates under steady state conditions as compared to the transient reactivity on the catalyst pre-saturated with D(2). Limitations in D availability during the steady state lead to a very weak dependence of both reaction rates on the olefin pressure. In contrast, when the surface is initially saturated with D, the transient reaction rates of both pathways exhibit positive kinetic orders on the butene pressure. Cis-trans isomerization and hydrogenation show kinetic orders of +0.7 and +1.0 on the D(2) pressure, respectively. Increasing availability of D noticeably shifts the selectivity toward hydrogenation. These observations together with the analysis of the transient reaction behavior suggest that the activity and selectivity of the catalyst is strongly controlled by its ability to build up and maintain a sufficiently high concentration of D species under reaction conditions. The temperature dependence of the reaction rates indicates that higher activation energies are required for the hydrogenation pathway than for the cis-trans isomerization pathway, implying that different rate limiting steps are involved in the competing reactions.     

Detection of protease activities with the mass-spectrometry-assisted enzyme-screening (MES) system

The MALDI-MES provides a rapid, sensitive and reproducible alternative approach to existing analytical techniques for the detection of enzymatic activities that does not require a chromophore or radiolabeling. An improved method is presented, by which enzymes with defined substrate specificities can be detected with a MALDI mass spectrometer in complex protein fractions. In order to demonstrate the utility of the new method, in this study we describe the use of MALDI-MES to detect proteolytic activities in a protein extract from porcine renal tissue, which contained several thousand proteins as visualized by 2D electrophoresis. The analytical procedure is based on covalent immobilization of proteins to beads. By immobilizing proteins, autolytic and proteolytic degradation is prevented and the removal of those molecules from the protein fraction is achieved, which otherwise would interfere with the mass spectrometric detection of the enzymatic reaction products. The enzymatic activity is determined by incubating the immobilized proteins with a reaction-specific probe, followed by the analysis of the reaction mixture with the MALDI-MS after defined incubation times. The presence of the target enzyme is validated by locating a signal, which fits the molecular mass of the expected reaction product in the mass spectrum. To demonstrate how to detect proteolytic activities in this system, the reactions catalyzed by endopeptidase, angiotensin-converting enzyme, kallikrein, renin, and urotensin-converting enzyme were monitored. The experiments showed that the MALDI-MES method is sufficient according the quantification to investigate the effects of inhibitors. This is demonstrated using a specific renin inhibitor to inhibit an angiotensin-I generating enzyme activity in a renal protein extract.Abbreviations MALDI-MS matrix-assisted mass spectrometry - MES mass-spectrometry-assisted enzyme-screening system