Regina Palkovits

Bio-based polyesters with pyrrolidone and imidazole groups as a alternative to fossil-based polymers. Significant improvement in properties as solubility enhancers for poorly water-soluble active ingredients through the use of these new polymers.

Biomass presents an attractive resource for a sustainable production of platform chemicals and monomers. Especially N‐containing compounds are broadly utilized as solvents, in polymer production and as fine chemicals or pharmaceutics. An important compound is N‐vinyl‐pyrrolidone used for polyvinylpyrrolidone production (PVP). Today it is produced based on fossil acetylene via Reppe chemistry and vinylation. However, it can be accessed from biomass‐derived succinic acid by reductive amination with ethanolamine and hydrodeoxygenation followed by dehydration of the ethanol group to provide the vinyl functionality. Previous studies identified selective hydrodeoxygenation of the intermediate N‐(2‐hydroxyethyl)succinimide (HESim) as crucial to achieve high selectivity and yield. At the same time, an LCA study highlighted the significant impact of selective product formation on the CO ₂ ‐footprint of this route. This study discusses bimetallic Pt/X (X = V, Cu, Ni, Co, and Mo) catalysts supported on TiO ₂ for efficient hydrodeoxygenation of HESim. Aiming for high activity and overall performance, alternative metal combinations were screened and recycling experiments conducted. Combining Pt and Mo on TiO ₂ allowed achieving 97% HESim conversion and 95% yield of the two desired products N‐(2‐hydroxyethyl)‐2‐pyrrolidone (HEP) and 4‐hydroxy‐N‐(2‐hydroxyethyl)‐butanamide (HEBA). Accordingly, Pt/Mo on TiO ₂ outperforms the previous literature best performer based on a supported Pt/Re‐catalyst.

Solid molecular catalysts (SMCs) represent a promising class of photocatalysts. Here, we report the influence of distinct donor and acceptor moieties of terpyridine‐based SMCs on the photocatalytic hydrogen peroxide (H ₂ O ₂ ) production. An aromatic and linear donor proved to be advantageous due to its favorable optoelectrical properties, achieving an activity of 8.55 mmol g ⁻¹ h ⁻¹ under white light irradiation without any sacrificial agents. The variation of backbone functionalities (toluene (C), pyrrole (N), furan (O), and thiophene (S)) revealed the important role of charge stabilization in the acceptor units through inductive and mesomeric effects. Scaling up the reaction with the best performing SMC C2‐SP1 yielded a photocatalytic activity of 12.8 mmol g ⁻¹ h ⁻¹ (405 nm). To facilitate the transition from laboratory studies to practical applications, H ₂ O ₂ production has been successfully demonstrated under natural sunlight. Under optimized reaction conditions, concentrations of up to 108.3 mg L ⁻¹ were achieved, demonstrating the potential of SMCs for sustainable hydrogen peroxide generation.

This study presents a Rh@poly-dppe catalyst system that overcomes key limitations of heterogenized hydroformylation catalysts by enabling stable hydroformylation with minimized side reactions, low rhodium leaching, and sustained performance under continuous operation over extended reaction times. Immobilization of molecularly defined Rh species is achieved using a phosphine-functionalized porous organic polymer (poly-dppe) that acts as a solid macroligand for rhodium. The polymer architecture enables increased metal loadings while maintaining a well-defined molecular coordination environment. Systematic variation of the P/Rh ratio reveals its decisive role in balancing catalytic activity, regioselectivity, and metal retention. Comprehensive catalyst characterization provides insight into the nature of the immobilized rhodium species and their stability under reaction conditions. Transfer of the catalyst system to continuous operation demonstrates stable steady-state performance with low metal leaching. Overall, combining the well-defined coordination environment of a molecular rhodium catalyst with the simple recyclability of a solid heterogeneous catalyst highlights the suitability of phosphine-based porous organic polymers as platforms for solid molecular hydroformylation catalysts.

The electrochemical nitrate reduction to ammonia (eNO ₃ RR) is an important step toward sustainable ammonia synthesis. Despite a few challenges in securing sufficient nitrate sources for commercial scale production of ammonia, a key current focus is the search for a cost‐effective yet highly active catalyst. Here, we present physical vapor deposition as a quick and straightforward technique for producing a thin layer of cobalt deposits on copper foam which shows significant performance (95% FE _NH3 ) for eNO ₃ RR. The superior performance of the Co–Cu foam is proposed to arise from the synergistic impact of Co–Cu on the direct reduction of NO ₃ ⁻ to NH ₃ , coupled with the subsequent reduction of NO ₂ ⁻ produced on Cu sites.

Efficient utilization of solar energy remains paramount in the context of a more sustainable future. To enable rational design of heterogeneous photocatalysts, a deeper understanding of photoactive structures and reaction mechanisms is required. In this study, a modular semiconductor design platform along the axes of pyridine denticity and an amine functionalization is presented. In the model photocatalytic hydrogen peroxide synthesis, the best-performing catalyst achieves productivities upwards of 2.3 mmol h ^-1  g ^-1 under white light irradiation at 500 W m ^-2 . Through application as a coating, both apparent quantum yields (1.27%) and solar-to-chemical conversion efficiencies (0.28%) were significantly improved. In radical scavenging and EPR experiments, the modular design approach allows the correlation of catalyst structures with the formation of different radical species, and in turn, mechanistic pathways. On the basis of this knowledge, the decomposition of waste antibiotics is identified and demonstrated as suitable use-case. This work provides a template for the informed design of photocatalysts and the characterization of the underlying reaction mechanisms.

Ni-based catalysts are widely used for CO ₂ methanation due to their high activity comparable to noble metals and favorable cost. Herein, (La, Ce)Ox-supported Ni catalysts are prepared using incipient-wetness impregnation and sol-gel synthesis to investigate the effect of preparation method on catalyst properties, including basicity, crystallinity, electronic structure, and metal-support interactions. Compared to Ni/(La, Ce)Ox-IM prepared by impregnation, Ni/(La, Ce)Ox-SG prepared by sol-gel synthesis showed high activity with a CO2 conversion rate of 57.4 mmol CO2/molNi/s and 99.3% CH4 selectivity at 350 oC and 1 atm, and exhibited the lowest apparent activation energy among the catalysts studied. Comprehensive characterization pinpoints differences in domain size, Ni dispersion, as well as size and exposure of Ni(111) facets. Moreover, in-situ DRIFTS studies disclose a mechanistic difference in the CO2 methanation pathway, i.e., a dissociative pathway over the Ni/(La, Ce)Ox-SG, while an associative pathway prevails over Ni/(La, Ce)Ox-IM. In-situ time-resolved PDF measurements under reduction and methanation conditions with different H2/CO2 ratios revealed structural dynamics and Ni0 oxidation only over Ni/(La, Ce)Ox-SG at H2/CO2=1/1. In contrast, Ni/(La, Ce)Ox-IM remains unaffected. The reversible Ni0 oxidation in Ni/(La, Ce)Ox-SG is accompanied by an increased disorder in the La-doped ceria lattice, likely due to oxygen vacancy formation and oxygen migration from ceria to metallic Ni via the reverse oxygen spillover mechanism, indicating distinct differences in the metal-support interactions of the two catalysts.

Electrochemical reductive amination of acetone using Ag electrodes is strongly enhanced by 1 ppm Pb in the solution but the underlying mechanisms and the nature of the Pb species remain poorly understood. To understand how trace elements alter reaction pathways and enhance catalytic performance, the catalytic behavior of Pb traces in electrochemical hydrogenation was theoretically investigated. Using computational modeling, we examined the formation of Pb hydrides (PbH₂ and PbH₄) on the electrified silver surface at the highly reducing potential used experimentally and their reactivity either at the polarized surface or in the solution in proximity of the electrode, including for hydrogen transfer towards the imine intermediate in the electrocatalytic amination of acetone with methylamine. Our results highlight a key role of Pb hydride species (PbH₂ at the electrode surface or PbH₄ in the near-electrode solution) for the imine hydrogenation step. In the absence of Pb, hydrogenations directly on the Ag electrode by proton coupled electron transfer or by surface hydrides both suffer from high energy barriers, altogether explaining the experimental requirement of Pb traces for activity. One possible scenario is a dynamic cycle where PbH₄, a highly unstable compound, is formed by the reducing potential at the Ag electrode and acts as a short-lived hydrogen shuttle in the near-electrode solution, either homogeneously hydrogenating the imine or producing hydrogen evolution, by decomposition or interaction with water. Another scenario underlines PbH₂ as the main actor, formed on the electrode, and hydrogenating the imine on the Ag surface heterogeneously. This study proposes an original hypothesis for the role of Pb as a hydrogen transfer agent, offering a mechanistic understanding of its catalytic behavior. Our findings not only explain the enhanced efficiency and selectivity observed in Pb-catalyzed electrochemical hydrogenation but also open avenues for the rational design of advanced catalysts based on trace elements to optimize sustainable electrochemical processes.

In the context of a green H ₂ ‐based economy, chemical H ₂ carriers are essential for efficient H ₂ storage and transportation. Among H ₂ carriers, dimethyl ether (DME) is a promising candidate due to its characteristics, such as non‐toxicity, easy transportation, high H ₂ storage capacity, and its circular nature by the reusability of CO ₂ formed from DME steam reforming (DME SR). H ₂ stored in DME can be released via DME SR over a bifunctional catalyst, consisting of a solid acid and a metal‐based catalyst. The reaction conditions, in particular, the reaction temperature, are crucial for an efficient H ₂ release and depend on the catalysts employed. This concept paper first highlights DME synthesis by CO ₂ hydrogenation and then discusses in detail the advances for DME SR at temperatures below 300°C. The kinetic and thermodynamic limitations for DME SR as well as challenges due to side reactions are presented. Zeolites are discussed as promising candidates for low‐temperature applications for the DME hydrolysis step and current insights into structure–activity relationships are highlighted. Catalyst deactivation due to coking and possible regeneration strategies are presented and last, perspectives for developing optimized catalysts for low‐temperature DME SR are provided.

Palladium‐loaded phosphine polymers have been designed and used as solid molecular catalysts (SMCs) in telomerization reactions with isoprene and short alcohols. A novel tris‐(2‐methoxyphenyl)phosphine‐based polymer (pTOMPP), previously reported poly triphenylphosphine (pTPP) as well as TPP‐based polymers with trigonal and tetragonal linkers were tested either pre‐loaded or in‐situ‐loaded. The novel polymer pTOMPP proved to be an excellent support material during in‐situ‐loading, outperforming triphenylphosphine based polymers. Surprisingly pre‐loaded SMCs resulted in significantly lower activity. XAS studies reveal that the enhanced activity of Pd/pTOMPP is due to the coordination sphere of Pd on the polymer showing a higher contribution of Pd‐P bonds forming, whereas XAS spectra of Pd/pTPP show a higher contribution of inactive Pd‐acac bonds. Especially pre‐loaded polymers show little Pd‐P interactions.