Catalysis Today最新文献

Surface reconstituted metal-organic frameworks (MOFs) offer appealing properties for electrocatalysis due to their unique structural and compositional advantages. In this work, a controlled potential-induced reconstruction of a two-dimensional cobalt metal-organic framework for boosting oxygen evolution reaction in alkaline media is reported. The current MOF is shown to undergo a partial structural transformation that generates a heterogeneous system, where the original MOF coexists with an oxyhydroxide phase. In fact, the potential-induced stabilization of Co(III) metal centers in the MOF is crucial for delaying its full degradation in alkaline media. This partial retention of the Co(III)MOF phase in the so-derived heterogeneous catalyst has been demonstrated to be decisive for boosting the alkaline electrocatalytic oxygen evolution reaction (OER), displaying superior OER activity in terms of both thermodynamic and kinetic merits compared to the benchmark IrO₂ and RuO₂ electrocatalysts and the prototypical cobalt (oxy)hydroxides, with a Tafel slope of 52 mV dec⁻¹ and a turnover frequency (TOF) of 6.8 s⁻¹ at 450 mV. Remarkably, the generated final product is stable, exhibiting high robustness and long durability for long-term OER electrolysis. This work provides new insight into the impact of the reconstruction of a MOF for alkaline OER under typical electrochemical conditions, which ultimately benefits the rational design of MOF-based catalysts with high electrocatalytic activity for oxidation reactions.

The esterification of levulinic acid (LA) to alkyl levulinate esters from biomass by heterogeneous acid catalysis is a potential chemical route for the sustainable production of high value-added products. Acidic zeolites are promising catalysts for this conversion due to their unique pore structures, high selectivity and strong acidity. In this work, we use Density Functional Calculations (DFT) to study the reaction mechanisms for the esterification of LA with MeOH on H-Beta zeolite. We have studied two mechanisms that we consider relevant to the formation of methyl levulinate in acidic zeolites, one involving an Eley-Rideal type mechanism and the other a Langmuir-Hinshelwood type mechanism. Since the activation energies of the rate-determining steps are quite similar, our results suggest that both mechanisms are favourable for this reaction, depending on how the LA and MeOH molecules are initially adsorbed.

Photocatalytic partial oxidation of tyrosol (Tyr) to hydroxytyrosol (Htyr) which is a valuable antioxidant compound, was carried out in a fully recirculated flow photoreactor under UVA light irradiation by using as photocatalyst bare or fluorinated TiO₂ immobilized on glass beads. The maximum selectivity towards Htyr obtained under optimized conditions in the presence of fluorinated TiO₂ at pH 8.7 was approximately 12 %. Reducing the residence time did not result in any further improvement of reaction selectivity due to the fast overoxidation of Htyr.

The photocatalytic reactor was then coupled with an adsorption unit containing a home-made adsorbent exposing amine-stabilized boronate moieties, which showed negligible interaction with Tyr but was capable of selectively binding Htyr on its surface. This allowed for the complete recirculation of the reactant Tyr to the reactor, while the desired product Htyr could be selectively removed from the reaction medium, significantly limiting its parasitic overreaction. Consequently, performing the reaction in the coupled system doubled the selectivity towards Htyr for all configurations, providing a maximum selectivity of 25 % under optimized conditions, which is twice the highest value ever reported for this photocatalytic reaction.

Finally, the kinetic experimental data were modeled using the Copasi software package to elucidate the reaction pathway and estimate the apparent kinetic parameters of the photocatalytic process, both alone and in combination with the adsorption unit. The simulated results showed excellent agreement with the experimental data.

For the first time the international symposium on group V elements included group IV and VI elements: titanium chromimu halfnium and chromium, molybdenum, and tungsten. This symposium series began in 1992 and it was originally dedicated to niobium compounds [1]. Three years later, again in Tokyo, the second symposium remained with niobium materials and catalysts [2]. After another three years, the symposium shifted to Rio de Janeiro and expanded to include vanadium and tantalum group V elements [3]. The symposium has been held every three years thereafter in Spain [4], [5], Hancock Massachusetts [6], Poland [7], Italy [8], and New Delhi in 2019 [9]. Due to COVID the 10th symposium, held in Montreal, was delayed by one year and it was expanded to include Group IV and VI elements.