Andrey V. Bukhtiyarov

Strong Metal–Support Interactions for Palladium Supported on TiO2 Catalysts in the Heterogeneous Hydrogenation with Parahydrogen

Parahydrogen‐induced polarization (PHIP) was successfully utilized to demonstrate the strong metal–support interaction (SMSI) effect for palladium supported on titania catalysts. Heterogeneous hydrogenation of 1,3‐butadiene over Pd/TiO2 catalysts led to the formation of 1‐ and 2‐butenes and butane, and hyperpolarized products were obtained if parahydrogen was used in the reaction. However, if the catalysts were reduced in H2 flow at 500 °C before the hydrogenation reaction, the observed polarization levels were significantly lower or even zero, which was indicative of the suppression of the pairwise addition of hydrogen route. This observation indicated the possibility to detect the SMSI effect by the PHIP technique. Moreover, by using X‐ray photoelectron spectroscopy it was shown that Pd is partially present as Pdδ+ after reduction under a hydrogen atmosphere at 500 °C. These results were confirmed by transmission electron microscopy, which revealed the formation of Pdδ+ and the dissolution of Pd in the titania lattice.

Aqueous, Heterogeneous para-Hydrogen-Induced 15N Polarization

The successful transfer of para-hydrogen-induced polarization to 15N spins using heterogeneous catalysts in aqueous solutions was demonstrated. Hydrogenation of a synthesized unsaturated 15N-labeled precursor (neurine) with parahydrogen (p-H2) over Rh/TiO2 heterogeneous catalysts yielded a hyperpolarized structural analogue of choline. As a result, 15N polarization enhancements of over 2 orders of magnitude were achieved for the 15N-labeled ethyltrimethylammonium ion product in deuterated water at elevated temperatures. Enhanced 15N NMR spectra were successfully acquired at 9.4 and 0.05 T. Importantly, long hyperpolarization lifetimes were observed at 9.4 T, with a 15N T1 of ∼6 min for the product molecules, and the T1 of the deuterated form exceeded 8 min. Taken together, these results show that this approach for generating hyperpolarized species with extended lifetimes in aqueous, biologically compatible solutions is promising for various biomedical applications.

Frontispiece: Selective Single-Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Pd-In/Al2 O3 single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al2 O3 in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire 1 H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.

CO Adsorption on Reconstructed Ir(100) Surfaces from UHV to mbar Pressure: A LEED, TPD, and PM-IRAS Study

Clean and stable surface modifications of an iridium (100) single crystal, i.e., the (1 × 1) phase, the (5 × 1) reconstruction, and the oxygen-terminated (2 × 1)-O surface, were prepared and characterized by low energy electron diffraction (LEED), temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS) and polarization modulation IRAS (PM-IRAS). The adsorption of CO in UHV and at elevated (mbar) pressure/temperature was followed both ex situ and in situ on all three surface modifications, with a focus on mbar pressures of CO. The Ir(1 × 1) surface exhibited c(4 × 2)/c(2 × 2) and c(6 × 2) CO structures under low pressure conditions, and remained stable up to 100 mbar and 700 K. For the (2 × 1)-O reconstruction CO adsorption induced a structural change from (2 × 1)-O to (1 × 1), as confirmed by LEED, TPD, and IR. For Ir (2 × 1)-O TPD indicated that CO reacted with surface oxygen forming CO2. The (5 × 1) reconstruction featured a reversible and dynamic behavior upon CO adsorption, with a local lifting of the reconstruction to (1 × 1). After CO desorption, the (5 × 1) structure was restored. All three reconstructions exhibited CO adsorption with on-top geometry, as evidenced by IR. With increasing CO exposure the resonances shifted to higher wavenumber, due to adsorbate–adsorbate and adsorbate–substrate interactions. The largest wavenumber shift (from 2057 to 2100 cm–1) was observed for Ir(5 × 1) upon CO dosing from 1 L to 100 mbar.

Bimetallic Pd—Pt/γ-Al 2 O 3 catalysts for complete methane oxidation: the effect of the Pt: Pd ratio

Alumina-supported bimetallic Pt—Pd catalysts proved to be more active in the complete oxidation of methane than monometallic systems (Pt/Al2O3, Pd/Al2O3). The maximum activity of the bimetallic catalysts was achieved at ~40 at.% Pt in Pd on the catalyst surface. After the oxidation reaction, redistribution of platinum and palladium was observed in the active component of the catalysts with the degree of redistribution depending on the initial Pt: Pd ratio.