We report here the upcycling of PET (polyethylene terephthalate) waste via semihydrogenation to make ethyl 4-(hydroxymethyl)benzoate. The reaction is catalyzed by a ruthenium pincer catalyst at 80 °C in bioderived solvents – a combination of 2-methyl THF and ethanol. A detailed mechanistic investigation through organometallic and kinetic studies, as well as chemical exchange saturation transfer (CEST) NMR spectroscopy, provides insights into the nature of active species and factors that promote and inhibit the catalytic hydrogenation of PET. Using this mechanistic knowledge, a record high turnover number of >30 000 was achieved for the hydrogenative depolymerization of end-of-life PET waste (e.g., bottles and textiles). The semihydrogenation product, ethyl 4-(hydroxymethyl)benzoate, was utilized to make precursors of various known pharmaceutical drugs, an agrochemical, as well as a new and recyclable polyester. A cradle-to-gate life cycle assessment demonstrated that using PET waste as a feedstock for EHMB production significantly reduces the environmental footprint compared to the conventional route from p-toluic acid.

Cu-modified zeolites provide methane conversion to methanol with high selectivity under mild conditions. The activity of different Cu-sites for methane transformation is still under discussion. Herein, ZSM-5 zeolite has been loaded with Cu²⁺ cations (1.4 wt % Cu) as characterized by UV-vis DRS, EPR, EXAFS, and ¹H MAS NMR. It is inferred that Cu²⁺ cations, attached to the cation-exchange Al−O⁻−Si sites of the zeolite framework, can exist in the form of either isolated or paired Cu²⁺ sites. The transformation of methane to methanol on Cu²⁺/H-ZSM-5 has been verified by the observation of the methoxy species formation with ¹³C MAS NMR and FTIR spectroscopy. The related mechanisms have been analyzed by DFT calculations. The calculations show that the paired Cu²⁺ sites enable heterolytic C−H bond dissociation via the “alkyl” pathway resulting in methylcopper species, which however are not detected experimentally due to further rapid transformation to surface methoxy species through methyl radical formation and recombination with Si−O⁻Al site. Based on the obtained data, it has been concluded that methane transformation to methanol on paired Cu²⁺ sites, having no extra-framework oxygen ligand, is possible in Cu-modified zeolites. The pathways of Cu²⁺ cations regeneration with O₂ and H₂O have been experimentally explored.

Plastic waste is a major environmental issue; converting it directly into valuable chemicals by using catalysts is a promising alternative to plastic recycling. Here, we report the selective catalytic cracking of polypropylene (PP), a typical commodity plastic, to high-value light olefins (C2–C5), below pyrolytic temperature (290 °C) and without external hydrogen supply, by using zeolite catalysts. Among the H+-form zeolites with different structures, HMFI showed the highest yields of light hydrocarbons (C2–C5), of which light olefins (C2–C5) were the major products. The HMFI-catalyzed PP conversion was applicable to the upcycling of a model PP waste, resulting in a 61.9% light hydrocarbon yield. The results of catalytic and in situ IR experiments using model HMFI catalysts with a small amount of external Brønsted acid sites suggested that the Brønsted acid sites on the external surface of HMFI are indispensable for the PP conversion and are posited to be the active sites for the cracking of PP into short-chain (oligomeric) hydrocarbon species as intermediate products. Density functional theory analyses were conducted to determine plausible reaction pathways by adopting 2,4-dimethylheptene as the shortest unit of the oligomeric species. The obtained results show that the β-scission of 2,4-dimethylheptene by Brønsted acid sites yields isobutene and propylene (or a propyl alkoxide group) via carbocation intermediates with an activation energy below 118 kJ mol–1. Operando UV–vis and IR experiments under the reaction conditions, combined with ex situ 1H NMR and 13C NMR analyses of the spent catalyst, show that some of the olefins are further converted to light or heavy aromatics (coke deposit), probably via carbenium ion species.

Understanding how surface species evolve under reaction conditions is essential for improving catalyst design for efficient CO2 hydrogenation. This work combines systematic DFT calculations with grand canonical sampling to investigate the stability and reactivity of Ga–H species on β-Ga2O3 across a range of reaction conditions. Initial DFT studies reveal that when Ga–H species are present, they facilitate formate formation via a low-barrier pathway, largely independent of the surface termination or hydrogen site. However, grand canonical sampling shows that under a broad range of reaction conditions─especially at high oxygen chemical potentials associated with high water content─Ga–H species are thermodynamically inaccessible. Furthermore, adsorbed water molecules can block reactive sites, inhibiting CO2 activation even when hydrides are present. These findings suggest that the lack of accessible hydride species, rather than their intrinsic reactivity, could contribute to reduced catalytic performance of β-Ga2O3 under more oxidizing, high-conversion conditions.

Sulfated zirconium oxide (SZO) catalyzes the hydrogenolysis of isotactic polypropylene (iPP, Mw=13.3 kDa, Đ=2.4, <mmmm>=94 %) or high-density polyethylene (HDPE, Mn=2.5 kDa, Đ=3.6) to branched alkane products. We propose that this reactivity is driven by the pyrosulfate sites SZO, which open under mild conditions to transiently form adsorbed SO3 and sulfate groups. This adsorbed SO3 is a very strong Lewis acid that binds 15N-pyridine or triethylphosphineoxide (TEPO) (ΔEads>−39 kcal mol−1), reacts with Ph3CH to form Ph3C+, and mediates H/D exchange in dihydroanthracene-d4. DFT studies show that pyrosulfate sites open with a modest 26.1 kcal mol−1 barrier to form the adsorbed SO3 and sulfate in the presence of a tetramer of propylene. Hydride abstraction from the tertiary C−H in this model is exothermic and subsequent β-scission forms cleaved products. Analysis of the energetics provided here brackets the hydride ion affinity (HIA) of the adsorbed SO3 between 226.2 to 237.9 kcal mol−1, among largest values reported for a formally neutral Lewis acid. This study explains how SZO, a classic heterogeneous catalyst, can form carbocations by a redox neutral hydride abstraction reaction by very strong Lewis sites.

Simulation and systematic analysis of the surfaces of amorphous materials is a challenge for computational chemistry. For example, silica has found widespread industrial use as an adsorbent and catalyst support but available models for use with periodic DFT are limited in variety and representativeness of realistic materials. Herein we present a generic approach for the systematic construction of ensembles of amorphous materials surface models with varied roughness and termination characteristics. The power of the approach is shown with silica as the representative example. By combining MD simulations and Fourier-series-based randomization, bulk amorphous silica was modeled and cleaved to produce surfaces with systematically varied roughness and surface saturation. An automated saturation procedure resulted in surface models with silanol densities typical of high-temperature activation protocols in the range 0.35–2.00 OH nm−2, in excellent agreement with the experimental data on surface chemistry of dehydroxylated silica materials.

This chapter provides a brief introduction to computational chemistry in the context of zeolite research, emphasizing the capabilities and limitations of modern theoretical models for investigating their reactivity and chemical properties under operando conditions. A brief overview of the computational chemistry toolbox is given, followed by a discussion of state-of-the-art applications in zeolite chemistry and catalysis. This chapter also highlights the increasing impact of data-driven techniques, such as machine-learning potentials, in advancing computational methods in zeolite studies.

Chemical recycling of polyolefins represented by polyethylene (PE) and polypropylene (PP) via catalytic cracking has emerged as a promising strategy for converting waste plastics into valuable hydrocarbons. In this study, we investigated the selective hydrocracking of PP into light alkanes (C₁–C₅) using zeolite catalysts at 280 °C under 1 MPa H₂. An HMFI zeolite with high Al content exhibited the best catalytic performance among various zeolite catalysts tested. In situ DRIFTS comparing bare HMFI and externally-silylated HMFI suggested that the external surface Brønsted acid sites serve as the active sites for the cracking of PP. Combination of in situ DRIFTS and UV–vis spectroscopy analyses identified the formation and consumption of oligomeric species as a reaction intermediate during reaction. Density functional theory (DFT) calculations suggested that a route in which the carbocation and alkoxide intermediates generated by hydrocracking of PP undergo low-energy barrier transformations into gaseous products such as C₃ and C₄ hydrocarbons. This study advances the development of sustainable polyolefin recycling technologies.

Some of our recent developments and applications of algorithmic graph theory for extracting the physical and chemical properties of materials from molecular dynamics simulations are presented. From the chemical viewpoint, the power of graph theory is illustrated in the search for a catalyst's active sites at a silica solid surface. From the physical viewpoint, we present graph algorithms that recognize the structural motifs that exist at the silica/liquid water interface. Statistical analyses of the instances of these surface–water motifs provide a detailed understanding of the structures and dynamics at the aqueous interface.

Organic electrochemistry is currently experiencing an era of renaissance, which is closely related to the possibility of carrying out organic transformations under mild conditions, with high selectivity, high yields, and without the use of toxic solvents. Combination of organic electrochemistry with alternative approaches, such as photo-chemistry was found to have great potential due to induced synergy effects. In this work, we propose for the first time utilization of plasmon triggering of enhanced and regio-controlled organic chemical transformation performed in photoelectrochemical regime. The advantages of the proposed route is demonstrated in the model amination reaction with formation of C−N bond between pyrazole and substituted benzene derivatives. Amination was performed in photo-electrochemical mode on the surface of plasmon active Au@Pt electrode with attention focused on the impact of plasmon triggering on the reaction efficiency and regio-selectivity. The ability to enhance the reaction rate significantly and to tune products regio-selectivity is demonstrated. We also performed density functional theory calculations to inquire about the reaction mechanism and potentially explain the plasmon contribution to electrochemical reaction rate and regioselectivity.

Supported rhenium (Re) catalysts are emerging as promising candidates for hydrogenation reactions, which are crucial in industrial processes such as biomass valorization, CO2 reduction, and petroleum refining. However, despite their broad application, the structural and mechanistic understanding of these systems remains limited. The strong oxophilic nature of Re, combined with its ability to adopt multiple oxidation states, complicates the characterization of the active species even with advanced experimental techniques. In this study, we employ density functional theory calculations, alongside ab initio thermodynamic analysis, to systematically explore the structural and electronic properties of single-atom Re catalysts on a TiO2 surface, providing insights that could inform the rational catalyst design. Our calculations reveal the formation of stable Re polyhydrides on the surface under hydrogen-rich conditions. Notably, even in highly reducing environments, Re species with low formal oxidation states are thermodynamically unfavorable. The stable Re species identified on TiO2 surfaces demonstrate high reactivity toward CO2 hydrogenation. The electronic properties and computed X-ray photoelectron spectroscopy (XPS) signatures of the feasible surface species are highly influenced by the ligand environment. This work highlights the limitation of routine interpretation of experimental XPS characterization data in terms of the formal oxidation state.

Rational plastic recycling is critical for addressing the environmental challenges associated with plastic waste. Among the various recycling methods, chemical recycling, particularly via homogeneous catalysis, holds promise for converting plastic waste into valuable products. Post-consumer polymer wastes could present a challenge for catalytic upcycling due to the structural inhomogeneity and functionalization of the polyolefin chains. The impact of substrate aging on the performance of the upcycling catalyst can be viewed as an “inverse problem” of heterogeneous catalysis and has not received sufficient attention in mechanistic studies on this subject. Herein, we present a density functional theory study on the dehydrogenative upcycling of polyethylene (PE) with different in-chain impurities, representing the chemistry of post-consumption PE wastes. We selected the (^tBu4POCOP)-Ir pincer complex catalyzed dehydrogenation of PE as our model reaction. The calculations reveal that common in-chain impurities found in PE, such as carbonyl, hydroxyl, epoxides, and chlorine atoms, inhibit the overall catalyst performance. These impurities form stable molecular complexes with the catalyst, leading to a substantial increase in the energy barriers of the initial reaction step, the C-H bond addition. We also observe that the reaction on the ideal crystalline PE is also impeded. However, highly distorted PE chains exhibit greater susceptibility toward the (^tBu4POCOP)-Ir catalyst. Our mechanistic studies demonstrated that the reaction on the side alkane chains is kinetically favorable compared with the reaction on the PE backbone. The study highlights the critical role of in-chain heterogenieties in the catalytic activation of polymer chains and provides valuable insights into the development of effective technologies for upcycling plastic waste.

The stoichiometric conversion of methane to methanol by Cu-exchanged zeolites can be brought to highest yields by the presence of extraframework Al and high CH₄ chemical potentials. Combining theory and experiments, the differences in chemical reactivity of monometallic Cu-oxo and bimetallic Cu-Al-oxo nanoclusters stabilized in zeolite mordenite (MOR) are investigated. Cu-L₃ edge X-ray absorption near-edge structure (XANES), infrared (IR), and ultraviolet-visible (UV-vis) spectroscopies, in combination with CH₄ oxidation activity tests, support the presence of two types of active clusters in MOR and allow quantification of the relative proportions of each type in dependence of the Cu concentration. Ab initio molecular dynamics (MD) calculations and thermodynamic analyses indicate that the superior performance of materials enriched in Cu-Al-oxo clusters is related to the activity of two μ-oxo bridges in the cluster. Replacing H₂O with ethanol in the product extraction step led to the formation of ethyl methyl ether, expanding this way the applicability of these materials for the activation and functionalization of CH₄. We show that competition between different ion-exchanged metal-oxo structures during the synthesis of Cu-exchanged zeolites determines the formation of active species, and this provides guidelines for the synthesis of highly active materials for CH₄ activation and functionalization.

The reactivity theories and characterization studies for metal-containing zeolites are often focused on probing the metal sites. We present a detailed computational study of the reactivity of Zn-modified BEA zeolite towards C-H bond activation of the methane molecule as a model system that highlights the importance of representing the active site as the whole reactive ensemble integrating the extra-framework Zn_EF²⁺ cations, framework oxygens (O_F²⁻), and the confined space of the zeolite pores. We demonstrate that for our model system the relationship between the Lewis acidity, defined by the probe molecule adsorption energy, and the activation energy for methane C-H bond cleavage performs with a determination coefficient R² = 0.55. This suggests that the acid properties of the localized extra-framework cations can be used only for a rough assessment of the reactivity of the cations in the metal-containing zeolites. In turn, studying the relationship between the activation energy and pyrrole adsorption energy revealed a correlation, with R² = 0.80. This observation was accounted for by the similarity between the local geometries of the pyrrole adsorption complexes and the transition states for methane C-H bond cleavage. The inclusion of a simple descriptor for zeolite local confinement allows transferability of the obtained property-activity relations to other zeolite topologies. Our results demonstrate that the representation of the metal cationic species as a synergistically cooperating active site ensembles allows reliable detection of the relationship between the acid properties and reactivity of the metal cation in zeolite materials.

Selective dimerization of ethene to 2-butene on Zn2+-containing ZSM-5 zeolite (Zn2+/ZSM-5) at 296-523 K has been discovered. The intermediate but-3-en-1-ylzinc species is identified with 13C CP/MAS NMR and Fourier transform infrared spectroscopy. The density functional theory study of two alternative dimerization pathways reveals that the intermediate is formed with the involvement of the saturated bridged dimeric Zn-(CH2)4-O species. It is also shown that ethene conversion to 2-butene increases with the increase in the quantity of Brønsted acid sites in Zn2+/ZSM-5 zeolite; however, the selectivity of the reaction decreases. The results obtained are of potential interest for developing industrially relevant Zn-containing zeolite catalysts for the selective conversion of ethene to 2-butene.

The influence of the model and method choice on the DFT predicted 13C NMR chemical shifts of zeolite surface methoxide species has been systematically analyzed. Twelve 13C NMR chemical shift calculation protocols on full periodic and hybrid periodic-cluster DFT calculations with varied structural relaxation procedures are examined. The primary assessment of the accuracy of the computational protocols has been carried out for the Si-O(CH3)-Al surface methoxide species in ZSM-5 zeolite with well-defined experimental NMR parameters (chemical shift, δ(13C) value) as a reference. Different configurations of these surface intermediates and their location inside the ZSM-5 pores are considered explicitly. The predicted δ value deviates by up to ±0.8 ppm from the experimental value of 59 ppm due to the varied confinement of the methoxide species at different zeolite sites (model accuracy). The choice of the exchange-correlation functional (method accuracy) introduces ±1.5 ppm uncertainty in the computed chemical shifts. The accuracy of the predicted 13C NMR chemical shifts for the computational assignment of spectral characteristics of zeolite intermediates has been further analyzed by considering the potential intermediate species formed upon methane activation by Cu/ZSM-5 zeolite. The presence of Cu species in the vicinity of surface methoxide increases the prediction uncertainty to ±2.5 ppm. The full geometry relaxation of the local environment of an active site at an appropriate level of theory is critical to ensure a good agreement between the experimental and computed NMR data. Chemical shifts (δ) calculated via full geometry relaxation of a cluster model of a relevant portion of the zeolite lattice site are in the best agreement with the experimental values. Our analysis indicates that the full geometry optimization of a cluster model at the PBE0-D3/6-311G(d,p) level of theory followed by GIAO/PBE0-D3/aug-cc-pVDZ calculations is the most suitable approach for the calculation of 13C chemical shifts of zeolite surface intermediates.