Reaction-Induced Metal-Metal Oxide Interactions in Pd-In2O3/ZrO2 Catalysts Drive Selective and Stable CO2 Hydrogenation to Methanol

Ternary Pd-In₂O₃/ZrO₂ catalysts exhibit technological potential for CO₂-based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd-In₂O₃/ZrO₂ systems prepared by wet impregnation evolves under CO₂ hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal-metal oxide interaction energetics. The proximity of InPd_x alloy particles decorated by InO_x layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction-induced restructuring in complex CO₂ hydrogenation catalysts and offer insights into the optimal integration of acid-base and redox functions for practical implementation.     

Coupling of sequential injection with liquid chromatography for the automated derivatization and on-line determination of amino acids

The principle of sequential injection (SI) was exploited to develop a fully automated pre-column derivatization procedure combined on-line to liquid chromatography (LC). Using SI-LC derivatization 14 amino acids were determined fluorimetrically in pharmaceuticals with o-phthaldialdehyde (OPA) as the derivatization reagent. The SI system was used for the handling of samples and reagents, on-line mixing and introduction to the LC injection system. Chemical (pH and reagents concentrations) and instrumental variables (sample and reagent volumes, reaction time and flow rate) were optimized to attain the highest reaction yield and detector signal. Reversed phase chromatographic resolution of 14 amino acids was achieved within 35 min using gradient elution. The automated operation of the coupled SI-LC system resulted in very satisfactory performance. The method was applied for the simultaneous determination of amino acids in pharmaceutical formulations.     

Singlet Oxygen‐Induced Furan Oxidation for Site‐Specific and Chemoselective Peptide Ligation

A novel chemoselective ligation methodology has been developed for the facile construction of peptide‐based fluorescent probes. Furan‐containing peptides were activated by singlet oxygen and covalently engaged by nitrogen nucleophiles to yield stable conjugates. Singlet oxygen was compatible with sensitive amino acid residues within the peptides and a range of fluorophores, bearing different functionalities, were successfully incorporated, illustrating the broad scope of the developed strategy.     

Incorporation of a monolithic column into sequential injection system for drug-protein binding studies

A sequential injection analysis (SIA) manifold was incorporated with a monolithic strong anion-exchanger disk for on-line drug-protein interaction studies. The antibiotic ciprofloxacin (CF) was selected as a model drug compound. The separation principle was based on the strong retention of bovine serum albumin (BSA) on the monolithic strong anion-exchanger and the liberation/release of the free form of the drug. Elution of the retained BSA was easily achieved by delivering a different mobile phase via the SIA manifold. The type of functional group of the monolithic support, the breakthrough volume and the injected volumes of CF and BSA were studied and optimized. The influence of the variation of incubation time was studied in on-line binding assays. Scatchard plot was employed to obtain the number of binding sites and the equilibrium binding constants. For the off-line study of the CF-BSA binding, two binding classes were determined with constants of (3.16+/-0.21)x10(6)M(-1) and (1.27+/-0.48)x10(4)M(-1) and 6.1+/-1.3 and 17.8+/-3.9 binding sites per class, respectively. In non-equilibrium binding experiments the binding rate constant was k(1)=785 M(-1)min(-1). All measurements were monitored with fluorescence (lambda(ext)=300 nm, lambda(em)=460 nm) and spectrophotometric detection (lambda=280 nm). To evaluate the accuracy of the developed method the obtained results were compared versus ultrafiltration experiments and were found in good agreement.     

Cooperative Jahn-Teller distortion, phase transitions, and weak ferromagnetism in the KCrF3 perovskite

At ambient conditions, the ternary fluoride with formula KCrF3 adopts a perovskite-type structure and incorporates the Jahn-Teller active Cr2+ (d4) whose electronic configuration and magnetic response are analogous to those of Mn3+ (d4) and Cu2+ (d9). These ingredients make it an attractive system to study owing to the striking similarities with LaMnO3 and the expected strong interplay between spin, orbital, and structural ordering phenomena. Indeed, probing the properties of KCrF3 as a function of temperature (5 < T < 300 K) has revealed a structurally and magnetically far richer phase diagram than hitherto supposed. We found that KCrF3 exhibits large cooperative Jahn-Teller distortions which are driven by orbital ordering, a series of temperature induced complex structural transitions, and weak ferromagnetism which is reminiscent of what is observed in LaMnO3.     

Solvent-dependent changes in the ene reaction of RTAD with alkenes: the cyclopropyl group as a mechanistic probe

[reaction: see text] The vinylcyclopropyl moiety was used as an efficient probe to test mechanistic possibilities of the triazolinedione-alkene ene reaction. In non-hydroxylic solvents, this reaction afforded only the ene adducts via a closed three-membered aziridinium imide (AI) intermediate, whereas in hydroxylic solvents a dipolar intermediate is favored and trapped by the cyclopropyl moiety to form the corresponding cyclopropyl-rearranged solvent-trapped adducts.     

MIP-based decomposition strategies for large-scale scheduling problems in multiproduct multistage batch plants: A benchmark scheduling problem of the pharmaceutical industry

An efficient systematic iterative solution strategy for solving real-world scheduling problems in multiproduct multistage batch plants is presented. Since the proposed method has its core a mathematical model, two alternative MIP scheduling formulations are suggested. The MIP-based solution strategy consists of a constructive step, wherein a feasible and initial solution is rapidly generated by following an iterative insertion procedure, and an improvement step, wherein the initial solution is systematically enhanced by implementing iteratively several rescheduling techniques, based on the mathematical model. A salient feature of our approach is that the scheduler can maintain the number of decisions at a reasonable level thus reducing appropriately the search space. A fact that usually results in manageable model sizes that often guarantees a more stable and predictable optimization model behavior. The proposed strategy performance is tested on several complicated problem instances of a multiproduct multistage pharmaceuticals scheduling problem. On average, high quality solutions are reported with relatively low computational effort. Authors encourage other researchers to adopt the large-scale pharmaceutical scheduling problem to test on it their solution techniques, and use it as a challenging comparison reference.     

Uptake of n-hexane, 1-butene, and toluene by Au/Pt bimetallic surfaces: a tool for selective sensing of hydrocarbons under high-vacuum conditions

The dissociative adsorption and decomposition on a range of metal surfaces of an alkane, an alkene, and an aromatic, all representative of species present in an important technological application, has been studied under conditions relevant to selective gas sensing based on solid electrolyte potentiometry. At 870 K, pure polycrystalline Pt surfaces do not discriminate between n-hexane, toluene, and 1-butene: graphitic carbon accumulation occurs at almost the same rate. However, by varying the composition of polycrystalline bimetallic Pt/Au surfaces, good discrimination between these species can be achieved. Thus at a nominal surface composition of approximately 75% Au (XPS), good selectivity toward 1-butene and toluene uptake is achieved, with essentially no response to n-hexane. At approximately 80% Au the system is selective to 1-butene alone. Particular merits of these systems include good high-temperature stability and good tunability of their chemical selectivity. This makes possible the development of array devices in which the elements have overlapping but different selectivity profiles.     

Linearly implicit methods for nonlinear evolution equations

Summary.  We construct and analyze combinations of rational implicit and explicit multistep methods for nonlinear evolution equations and extend thus recent results concerning the discretization of nonlinear parabolic equations. The resulting schemes are linearly implicit and include as particular cases implicit–explicit multistep schemes as well as the combination of implicit Runge–Kutta schemes and extrapolation. We establish optimal order error estimates. The abstract results are applied to a third–order evolution equation arising in the modelling of flow in a fluidized bed. We discretize this equation in space by a Petrov–Galerkin method. The resulting fully discrete schemes require solving some linear systems to advance in time with coefficient matrices the same for all time levels. Received October 22, 2001 / Revised version received April 22, 2002 / Published online December 13, 2002 Mathematics Subject Classification (1991): Primary 65M60, 65M12; Secondary 65L06 Correspondence to: G. Akrivis