Correction: Propane to olefins tandem catalysis: a selective route towards light olefins production.

Correction for 'Propane to olefins tandem catalysis: a selective route towards light olefins production' by Matteo Monai et al., Chem. Soc. Rev., 2021, 50, 11503-11529, https://doi.org/10.1039/D1CS00357G.

Propane to olefins tandem catalysis: a selective route towards light olefins production.

On-purpose synthetic routes for propylene production have emerged in the last couple of decades in response to the increasing demand for plastics and a shift to shale gas feedstocks for ethylene production. Propane dehydrogenation (PDH), an efficient and selective route to produce propylene, saw booming investments to fill the so-called propylene gap. In the coming years, however, a fluctuating light olefins market will call for flexibility in end-product of PDH plants. This can be achieved by combining PDH with propylene metathesis in a single step, propane to olefins (PTO), which allows production of mixtures of propylene, ethylene and butenes, which are important chemical building blocks for a.o. thermoplastics. The metathesis technology introduced by Phillips in the 1960s and mostly operated in reverse to produce propylene, is thus undergoing a renaissance of scientific and technological interest in the context of the PTO reaction. In this review, we will describe the state-of-the-art of PDH, propylene metathesis and PTO reactions, highlighting the open challenges and opportunities in the field. While the separate PDH and metathesis reactions have been extensively studied in the literature, understanding the whole PTO tandem-catalysis system will require new efforts in theoretical modelling and operando spectroscopy experiments, to gain mechanistic insights into the combined reactions and finally improve catalytic selectivity and stability for on-purpose olefins production.

Identification of extremely hard coke generation by low-temperature reaction on tungsten catalysts via Operando and in situ techniques.

The coke formation in the catalytic system mainly cause to the catalyst deactivate resulting the dramatic decreasing of the catalyst performance then the catalyst regeneration was required. In this study, adding MgO physically mixed with WO3/SiO2 catalysts were prepared and compared with the ones prepared by physically mixing with SiO2. Adding MgO affected the generation of new species of coke deposited on WO3/SiO2 and MgO itself. Comparing the reaction temperature when adding MgO between at 300 and 450 °C, the different pathway of reaction and the coke formation were found. At 450 °C, the metathesis reaction was more pronounced and the lower temperature of coke deposited on WOx/SiO2 was found. Surprisingly, the extremely hard coke occurred during reaction at 300 °C that the maxima of coke formation was found over 635 °C. This due to the fact that the reduction of reaction temperature from 450 to 300 °C affected the decreasing of the metathesis activity. Conversely, the increasing of dimerization and isomerization of butenes-isomer was observed especially 1-butene and iso-butene. Thus, it could suggest that those quantity of them play the important role to generate the charged monoenyl or cyclopentenyl species by participating with ethene through the dimerization, resulting in the formation of extremely hard coke.

Role of Al in Na-ZSM-5 zeolite structure on catalyst stability in butene cracking reaction.

The Na-ZSM-5 catalysts (SiO2/Al2O3 molar ratio = 20, 35, and 50) were prepared by rapid crystallization method to investigate their performance in butene cracking reaction. The XRD, XRF, NH3-TPD, FT-IR, TPO, UV-Vis, and 1H, 27Al, 29Si MAS NMR techniques were used to identify the physical and chemical properties of Na-ZSM-5 catalysts. The silanol group (Si-OH) was the main acid site of Na-ZSM-5, and it was proposed to be the active site for the butene cracking reaction. The butene conversion and coke formation were associated with the abundance of silanol groups over the Na-ZSM-5 catalyst. The dealumination, resulting in the deformation of tetrahedral framework aluminum species was a key factor for Na-ZSM-5 catalyst deactivation, because of the Si-O-Al bond breaking and formation of Si-O-Si bond. The stability of the Si-O-Al bond was linked to the molar number of sodium since the Na atom interacts with the Si-O-Al bond to form Si-ONa-Al structure, which enhances the stability of the silanol group. Therefore, the Si-ONa-Al in zeolite framework was an essential structure to retain the catalyst stability during the reaction. The Na-ZSM-5 with the lowest SiO2/Al2O3 molar ratio showed the best performance in this study resulting the highest propylene yield and catalyst stability.

Intrinsic kinetic study of 1-butene isomerization over magnesium oxide catalyst via a Berty stationary catalyst basket reactor.

In this work, we studied the intrinsic kinetics of 1-butene isomerization over a commercial MgO catalyst using a Berty-type reactor (gradient-less recycle reactor). The Berty-type reactor has a behavior equivalent to a continuous stirred tank reactor (CSTR) with perfect mixing. The experimental results from this reactor were selected in a range in the absence of external and internal mass- and heat-transfer resistances, thereby representing the intrinsic kinetics. The 1-butene isomerization was carried out under atmospheric pressure, a WHSV of 1.05-5.47 h-1, and the reaction temperature from 350 °C to 450 °C. The kinetic models were established on the basis of different mechanisms for 1-butene isomerization over MgO. The results showed that the LHHW kinetic model provided the best agreement with the experimental data. The reactions involve three steps, including (1) adsorption of 1-butene on the active site, (2) the chemical surface reactions of 1-butene to trans- and cis-2-butene, and (3) the desorption of trans- and cis-2-butene. The surface reactions were assumed to be the rate-determining step. The percentage error of all predicted values was less than 5% under the studied operating conditions.

Halogen substitutions leading to enhanced oxygen evolution and oxygen reduction reactions in metalloporphyrin frameworks.

The oxygen evolution and oxygen reduction reactions (OER and ORR, respectively) are important in the field of renewable and clean energy, particularly for hydrogen production and fuel cells. These applications have so far been limited because of the high price of the catalysts and the energy loss due to overpotentials. Hence, non-precious metal catalysts with high efficiency toward the OER/ORR are desirable. In this work, we employ density functional theory (DFT) calculations to study the OER/ORR on metalloporphyrin and halogenated metalloporphyrin frameworks. The free energies of the reaction intermediates, including OH, O and OOH, were measured on 14 metal sites (Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Ir, Pt and Au) of the metalloporphyrin frameworks. Adsorption free energy relations were found and used to establish the reaction trend. The group 9 metals, namely Co, Rh and Ir, turn out to be potential candidates for both the OER and ORR because they provide intermediate free energies close to those of an ideal catalyst. The substitution of halogen atoms at the beta-positions of the metalloporphyrins of group 9 metals modifies the adsorption free energies of the intermediates so that they become closer to the ideal values and in turn reduce the OER and ORR overpotentials. After functionalization, Co-Por-F provides the lowest ORR overpotential and reduces the OER overpotential, approaching the value for an expensive Ir catalyst. Analysis of the electronic structure shows that controlling the d-band splitting by chemical manipulation of the single active site catalyst can be the key to enhancing the efficiency of these reactions.

Coordinatively Unsaturated Metal-Organic Frameworks M3(btc)2 (M = Cr, Fe, Co, Ni, Cu, and Zn) Catalyzing the Oxidation of CO by N2O: Insight from DFT Calculations.

The oxidation of CO by N2O over metal-organic framework (MOF) M3(btc)2 (M = Fe, Cr, Co, Ni, Cu, and Zn) catalysts that contain coordinatively unsaturated sites has been investigated by means of density functional theory calculations. The reaction proceeds in two steps. First, the N-O bond of N2O is broken to form a metal oxo intermediate. Second, a CO molecule reacts with the oxygen atom of the metal oxo site, forming one C-O bond of CO2. The first step is a rate-determining step for both Cu3(btc)2 and Fe3(btc)2, where it requires the highest activation energy (67.3 and 19.6 kcal/mol, respectively). The lower value for the iron compound compared to the copper one can be explained by the larger amount of electron density transferred from the catalytic site to the antibonding of N2O molecules. This, in turn, is due to the smaller gap between the highest occupied molecular orbital (HOMO) of the MOF and the lowest unoccupied molecular orbital (LUMO)  of N2O for Fe3(btc)2 compared to Cu3(btc)2. The results indicate the important role of charge transfer for the N-O bond breaking in N2O. We computationally screened other MOF M3(btc)2 (M = Cr, Fe, Co, Ni, Cu, and Zn) compounds in this respect and show some relationships between the activation energy and orbital properties like HOMO energies and the spin densities of the metals at the active sites of the MOFs.

Tailoring Metalloporphyrin Frameworks for an Efficient Carbon Dioxide Electroreduction: Selectively Stabilizing Key Intermediates with H-Bonding Pockets.

The electrocatalytic reduction of carbon dioxide (CO2ER) is a great challenge within the field of energy and environmental research. Competing reactions, including hydrogen evolution reactions (HER) and surface oxidation, limit the conversion of CO2ER at low overpotentials. This is because these competing reactions produce intermediates (adsorbed H and OH) with chemical bonds similar to those formed in CO2ER (adsorbed COOH and OCHO). Here, we report the adsorption free energies of CO2ER and competitive intermediates within H-bonding functionalized metalloporphyrin frameworks using first-principles calculations. The functionalized frameworks shift the scaling relation of adsorption free energies to favor the CO2ER intermediates rather than the HER. Inspired by molecular catalysts, we proposed and studied H-bonding interfaces that specifically stabilize the target intermediates of the CO2ER. The selective H-bonding stabilization reduced the limiting potential for CO2ER by up to 0.2-0.3 V. Our results agree with previous experiments that found that cobalt- and iron-based metalloporphyrins exhibited the most promising catalytic activity in CO2-to-CO reduction, with small potential barriers for the adsorbed COOH intermediate. In addition, embedding the functionalized metalloporphyrin moieties in a rigid framework structure acted to enhance the CO2ER selectivity by preventing the porphyrin from stacking and keeping H-bonding interfaces in close proximity to only CO2ER intermediates. Improved selectivity to the desired CO2ER was achieved through three steps: first by systematically screening for metal centers, second by creating an ideal H-bonding environment, and finally by using a rigid macrocycle ring structure.

Ethylene Epoxidation with Nitrous Oxide over Fe-BTC Metal-Organic Frameworks: A DFT Study.

The epoxidation of ethylene with N2 O over the metal-organic framework Fe-BTC (BTC=1,3,5-benzentricarboxylate) is investigated by means of density functional calculations. Two reaction paths for the production of ethylene oxide or acetaldehyde are systematically considered in order to assess the efficiency of Fe-BTC for the selective formation of ethylene oxide. The reaction starts with the decomposition of N2 O to form an active surface oxygen atom on the Fe site of Fe-BTC, which subsequently reacts with an ethylene molecule to form an ethyleneoxy intermediate. This intermediate can then be selectively transformed either by 1,2-hydride shift into the undesired product acetaldehyde or into the desired product ethylene oxide by way of ring closure of the intermediate. The production of ethylene oxide requires an activation energy of 5.1 kcal mol-1 , which is only about one-third of the activation energy of acetaldehyde formation (14.3 kcal mol-1 ). The predicted reaction rate constants for the formation of ethylene oxide in the relevant temperature range are approximately 2-4 orders of magnitude higher than those for acetaldehyde. Altogether, the results suggest that Fe-BTC is a good candidate catalyst for the epoxidation of ethylene by molecular N2 O.

Engineering Transition-Metal-Coated Tungsten Carbides for Efficient and Selective Electrochemical Reduction of CO2 to Methane.

The design of catalysts for CO2 reduction is challenging because of the fundamental relationships between the binding energies of the reaction intermediates. Metal carbides have shown promise for transcending these relationships and enabling low-cost alternatives. Herein, we show that directional bonding arising from the mixed covalent/metallic character plays a critical role in governing the surface chemistry. This behavior can be described by consideration of individual d-band components. We use this model to predict efficient catalysts based on tungsten carbide with a sub-monolayer of iron adatoms. Our approach can be used to predict site-preference and binding-energy trends for complex catalyst surfaces.

Sulfides: chemical ionization induced fragmentation studied with proton transfer reaction-mass spectrometry and density functional calculations.

We report the energy-dependent fragmentation patterns upon protonation of eight sulfides (organosulfur compounds) in Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Studies were carried out, both, experimentally with PTR-MS, and with theoretical quantum-chemical methods. Charge retention usually occurred at the sulfur-containing fragment for short chain sulfides. An exception to this is found in the unsaturated monosulfide allylmethyl sulfide (AMS), which preferentially fragmented to a carbo-cation at m/z 41, C3H5(+). Quantum chemical calculations (DFT with the M062X functional 6-31G(d,p) basis sets) for the fragmentation reaction pathways of AMS indicated that the most stable protonated AMS cation at m/z 89 is a protonated (cyclic) thiirane, and that the fragmentation reaction pathways of AMS in the drift tube are kinetically controlled. The protonated parent ion MH(+) is the predominant product in PTR-MS, except for diethyl disulfide at high collisional energies. The saturated monosulfides R-S-R' (with R

Density functional theory study of the carbonyl-ene reaction of encapsulated formaldehyde in Cu(I), Ag(I), and Au(I) exchanged FAU zeolites.

Carbonyl-ene reactions, which involve C-C bond formation, are essential in many chemical syntheses. The formaldehyde-propene reaction catalyzed by several of the group 11 metal cations, Cu(+), Ag(+), and Au(+) exchanged on the faujasite zeolite (metal-FAU) has been investigated by density functional theory at the M06-L/6-31G(d,p) level. The Au-FAU exhibits a higher activity than the others due to the high charge transfer between the Au and the reactant molecules, even though it is located at a negatively charged site of the zeolite. This site enables it to compensate for the charge of the Au(+) ion. The NBO analysis reveals that the 6s orbital of the Au atom plays an important role, inducing a charge on the probe molecules. Moreover, the effect of the zeolite framework makes the Au-FAU more active than the others by stabilizing the high charge induced transition structure. The activation energy of the reaction catalyzed by Au-FAU is 13.0 kcal/mol whereas that of Cu and Ag-FAU is found to be around 17 kcal/mol. The product desorption needs to be improved for Au-FAU; however, we suggest that catalysts with high charge transfer might provide a promising activity.

Oxidative dehydrogenation of propane over a VO2-exchanged MCM-22 zeolite: a DFT study.

The adsorption and the mechanism of the oxidative dehydrogenation (ODH) of propane over VO(2)-exchanged MCM-22 are investigated by DFT calculations using the M06-L functional, which takes into account dispersion contributions to the energy. The adsorption energies of propane are in good agreement with those from computationally much more demanding MP2 calculations and with experimental results. In contrast, B3LYP binding energies are too small. The reaction begins with the movement of a methylene hydrogen atom to the oxygen atom of the VO(2) group, which leads to an isopropyl radical bound to a HO-V-O intermediate. This step is rate determining with the apparent activation energy of 30.9 kcal mol(-1), a value within the range of experimental results for ODH over other silica supports. In the propene formation step, the hydroxyl group is the more reactive group requiring an apparent activation energy of 27.7 kcal mol(-1) compared to that of the oxy group of 40.8 kcal mol(-1). To take the effect of the extended framework into account, single-point calculations on 120T structures at the same level of theory are performed. The apparent activation energy is reduced to 28.5 kcal mol(-1) by a stabilizing effect caused by the framework. Reoxidation of the catalyst is found to be important for the product release at the end of the reaction.