Catalyst For Carbonylation Research Articles

A density functional theory study on the mechanism of Dimethyl ether carbonylation over heteropolyacids catalyst

Dimethyl ether (DME) carbonylation is considered as a key step for a promising route to produce ethanol from syngas. Heteropolyacids (HPAs) are proved to be efficient catalysts for DME carbonylation. In this work, the reaction mechanism of DME carbonylation was studied theoretically by using density functional theory calculations on two typical HPA models (HPW, HSiW). The whole process consists of three stages: DME dissociative adsorption, insertion of CO into methoxyl group and formation of product methyl acetate. The activation barriers of all possible elementary steps, especially two possible paths for CO insertion were calculated to obtain the most favorable reaction mechanism and rate-limiting step. Furthermore, the effect of the acid strength of Bronsted acid sites on reactivity was studied by comparing the activation barriers over HPW and HSiW with different acid strength, which was determined by calculating the deprotonation energy, Mulliken population analyses and adsorption energies of pyridine.

Dimethyl ether Carbonylation over Mordenite zeolite modified by Alkyimidazolium ions

Acidic mordenite zeolite was modified with various alkyimidazolium ions with different sizes via ion-exchange and applied as dimethyl ether (DME) carbonylation catalysts. Introducing 1, 3-dimethylimidazolium ions into zeolite can selectively remove the acid sites in 12-membered ring (MR) channels, significantly enhancing the stability and activity. Additionally, ion-exchange with organic ions was used to control the acid site distributions to separately investigate the DME carbonylation reaction in 8-MR and 12-MR channels. The reaction results indicated that the acid sites in 12-MR channels can concurrently catalyze the carbonylation and methanol-to-hydrocarbons (MTH) reactions, and MTH reactions seriously suppress the carbonylation activity in 8-MR channels.

Effect of microstructure of supports on catalytic activities of carbonylation catalysts

Nickel (Ni)-based catalysts supported by different active carbons (C) were prepared and used for vapor-phase carbonylation of ethanol. The microstructural properties of carbon supports were well investigated by using physical adsorption of nitrogen (N2), X-ray photoelectron spectroscopy, infrared spectrometry, Boehm titration and scanning electron microscopy. The catalytic activities of nickel/carbon catalysts were also studied. The results showed that wood charcoal had a large quantity of mesopores, a larger specific surface area and more oxygen (O)-containing groups such as carbonyl groups. The nickel catalyst supported by wood charcoal showed the highest catalytic activity, with 72.43% of ethanol conversion and 67.46% of product combined selectivity.

Quaternary phosphonium polymer-supported dual-ionically bound [Rh(CO)I3]2– catalyst for heterogeneous ethanol carbonylation

A single-Rh-site catalyst (Rh-TPISP) that was ionically-embedded on a P(V) quaternary phosphonium porous polymer was evaluated for heterogeneous ethanol carbonylation. The [Rh(CO)I3]2– unit was proposed to be the active center of Rh-TPISP for the carbonylation reaction based on detailed Rh L3-edge X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS), and Rh extended X-ray absorption fine structure (EXAFS) analyses. As the highlight of this study, Rh-TPISP displayed distinctly higher activity for heterogeneous ethanol carbonylation than the reported catalytic systems in which [Rh(CO)2I2]− is the traditional active center. A TOF of 350 h−1 was obtained for the reaction over [Rh(CO)I3]2–, with >95% propionyl selectivity at 3.5 MPa and 468 K. No deactivation was detected during a near 1000 h running test. The more electron-rich Rh center was thought to be crucial for explaining the superior activity and selectivity of Rh-TPISP, and the formation of two ionic bonds between [Rh(CO)I3]2– and the cationic P(V) framework ([P]+) of the polymer was suggested to play a key role in firmly immobilizing the active species to prevent Rh leaching.

High yield production of Co@N-doped carbon catalyst and its application in carbonylation of amines to form formamides

An economical and facile method for high-yield production of cobalt and nitrogen co-doped carbon by employing Cobalt salicylate/1,3-dimethylurea though pre-pyrolysis in high pressure is presented. The pre-pyrolysis process helped to produce more carbon, resulting in a weight loss of only 27% after twice pyrolysis. The as-prepared Co@N-doped carbon was charactered and applied as catalyst for the carbonylation of amines to form formamides for the first time in an atomic economic method. A new strategy for synthesis of Co@N-doped carbon materials which is scalable and of high-yield provides highly efficient cost-effective catalyst for economic carbonylation of amines to form formamides.

Cr-Phthalocyanine Porous Organic Polymer as an Efficient and Selective Catalyst for Mono Carbonylation of Epoxides to Lactones

A facile, one-pot design strategy to construct chromium(III)-phthalocyanine chlorides (Pc’CrCl) to form porous organic polymer (POP-Pc’CrCl) using solvent knitting Friedel-Crafts reaction (FCR) is described. The generated highly porous POP-Pc’CrCl is functionalized by post-synthetic exchange reaction with nucleophilic cobaltate ions to provide an heterogenized carbonylation catalyst (POP-Pc’CrCo(CO)4) with Lewis acid-base type bimetallic units. The produced porous polymeric catalyst is identical to that homogeneous counterpart in structure and coordination environments. The catalyst is very selective and effective for mono carbonylation of epoxide into corresponding lactone and the activities are comparable to those observed for a homogeneous Pc’CrCo(CO)4 catalyst. The (POP-Pc’CrCo(CO)4) also displayed a good catalytic activities and recyclability upon successive recycles.

Nitrogen-doped cobalt nanocatalysts for carbonylation of propylene oxide

Nitrogen-doped cobalt nanoparticles loaded on porous supports were developed for ring-opening carbonylation of propylene oxide. The catalysts were prepared by simply pyrolysis of Co(OAc)2/phenanthroline and supports. As proved by XPS combined with XRD and TEM characterizations, a higher amount of available Co-N sites were responsible for promoting the carbonylative activity. The selectivity of carbonylated products reached 93 %, which is comparable to previously reported cobalt carbonyl catalysts. The novel type of carbonylative catalyst also could be reused and revealed fine stability due to the continuous generation of active [Co(CO)4]− species during reaction.

Effect of Zr-doping on Pd/Ce Zr1−O2 catalysts for oxidative carbonylation of phenol

Abstract Ce–Zr solid solution (CexZr1−xO2, CZO) was prepared by the citric acid sol–gel method. The CZO was then used as a support for Pd/CZO catalysts for the oxidative carbonylation of phenol to diphenyl carbonate. The Pd/CZO catalyst showed enhanced activity and diphenyl carbonate selectivity compared with the Pd/CeO2 catalyst. The catalytic performance of Pd/CZO was influenced by the calcination temperature of the CZO support. X-ray diffraction, scanning electron microscopy, N2 adsorption–desorption measurements, X-ray photoelectron spectroscopy and H2 temperature-programmed reduction measurements were used to investigate the effects of Zr doping and calcination temperature. The catalytic performance of Pd/CZO and Pd/CeO2 for the oxidative carbonylation of phenol was affected by several factors, including the specific surface area, Ce3+ and/or oxygen vacancy content, oxygen species type and Pd(II) content of the catalyst. All these properties were influenced by Zr doping and the calcination temperature of the CZO support.

Copper supported on N‐heterocyclic carbene‐functionalized porous organic polymer for efficient oxidative carbonylation of methanol

A new heterogeneous catalyst for the oxidative carbonylation of methanol to dimethyl carbonate based on copper coordinated in N‐heterocyclic carbene‐functionalized porous organic polymer (Cu@PQP‐NHC) was presented. The solid catalyst that featured relatively large surface area, hierarchical pore structure, and excellent swelling property, was prepared via a facile copolymerization reaction of tetra‐vinylphosphonium salt and bis‐vinylimidazolium salt, followed by successful immobilization of CuCl. Accordingly, the resulting Cu@PQP‐NHC showed excellent catalytic performance for the oxidative carbonylation of methanol. A 10 mmol/l of Cu usage was sufficient for 9.3% conversion of methanol with a high TOF number of 57 h−1. Importantly, the catalyst was easily recovered by simple centrifugation, and could be reused up to 10 consecutive recycles without obvious loss of its initial activity. Also, the solid catalyst showed negligible Cu leaching during the recycling, and 99% Cu species was still retained after reusing 10 times. The results in this study highlights the advantages of porous organic polymer supported NHC‐Cu catalyst as a highly active and stable heterogeneous catalyst, providing a promising route for the synthesis of dimethyl carbonate.

Solution-Phase DNA-Compatible Pictet-Spengler Reaction Aided by Machine Learning Building Block Filtering.

SummaryThe application of machine learning toward DNA encoded library (DEL) technology is lacking despite obvious synergy between these two advancing technologies. Herein, a machine learning algorithm has been developed that predicts the conversion rate for the DNA-compatible reaction of a building block with a model DNA-conjugate. We exemplify the value of this technique with a challenging reaction, the Pictet-Spengler, where acidic conditions are normally required to achieve the desired cyclization between tryptophan and aldehydes to provide tryptolines. This is the first demonstration of using a machine learning algorithm to cull potential building blocks prior to their purchase and testing for DNA-encoded library synthesis. Importantly, this allows for a challenging reaction, with an otherwise very low building block pass rate in the test reaction, to still be used in DEL synthesis. Furthermore, because our protocol is solution phase it is directly applicable to standard plate-based DEL synthesis.

Highly active Pd containing EMT zeolite catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate

Abstract Palladium containing EMT zeolite catalyst (Pd/EMT) was prepared and used for the indirect oxidative carbonylation of methanol to dimethyl carbonate (DMC). The EMT zeolite was employed as a new catalyst support and compared with the conventional Pd containing FAU zeolite catalyst (Pd/FAU). The Pd/EMT in contrast to the Pd/FAU catalyst exhibited high intrinsic activity with the turnover frequency of 0.25 s−1 vs. 0.11 s−1. The Pd/EMT catalyst showed high CO conversion of 82% and DMC selectivity of 79%, that maintained for at least 130 h, while the activity of the Pd/FAU catalyst rapidly deteriorated within 12 h. The enhanced interactions between Pd and EMT zeolite inhibited the sintering of palladium clusters and maintained the Pd2+ active sites in the Pd/EMT catalyst. The stabilization of the mono-dispersed Pd clusters within the EMT zeolite is paramount to the excellent performance of the catalyst for the indirect oxidative carbonylation of methanol to DMC.

Evolution of the pore and framework structure of NaY zeolite during alkali treatment and its effect on methanol oxidative carbonylation over a CuY catalyst

Alkali treatment is widely used on aluminosilicate zeolites with high Si/Al ratios in order to fabricate mesopores in the framework. However, for zeolites with low Si/Al ratios, the effect of alkali treatment on the pore and framework structure needed further study. In this work, Y zeolite is treated with NaOH solutions of different concentrations and is used as the support for Cu-based catalysts for oxidative carbonylation of methanol to dimethyl carbonate. The physicochemical properties of the supports and corresponding catalysts are characterized by N2 adsorption–desorption, X-ray diffraction, X-ray fluorescence, transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction analyses. The results show that no obvious mesopores are formed under alkali treatment, even at high NaOH concentration. However, amorphous species present in the micropores of Y zeolite are removed, which increases the micropore surface area as well as the crystallinity. Simultaneously, the cage structure is partially destroyed, which also leads to a slight increase of the pore volume and surface area. The altered micropore structure eventually increases the content and accessibility of the exchanged Cu species, which is beneficial to the catalytic activity. When the concentration of NaOH is 0.6 M, the space time yield of dimethyl carbonate for the corresponding catalyst was 151.4 mg g−1 h−1 which is 3.3-fold higher than that of the untreated-Y-zeolite-supported Cu catalyst. However, further increasing the alkali treatment strength can seriously destroy the basic aluminosilicate structure of the Y zeolite and decrease its intrinsic ion-exchange capacity. This results in the formation of agglomerated CuO on the catalyst surface, which was not conducive to catalytic activity.

Light expands a catalyst's repertoire.

Visible light helps a Pd carbonylation catalyst both break and make carbon-halogen bonds

Photocatalytic CO2 Reduction under Visible-Light Irradiation by Ruthenium CNC Pincer Complexes.

Photocatalytic CO2 reduction using a ruthenium photosensitizer, a sacrificial reagent 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H), and a ruthenium catalyst were carried out. The catalysts contain a pincer ligand, 2,6-bis(alkylimidazol-2-ylidene)pyridine (CNC) and a bipyridine (bpy). The photocatalytic reaction system resulted in HCOOH as a main product (selectivity 70-80 %), with a small amount of CO, and H2 . Comparative experiments (a coordinated ligand (NCMe vs. CO) and substituents (tBu vs. Me) of the CNC ligand in the catalyst) were performed. The turnover number (TONHCOOH ) of carbonyl-ligated catalysts are higher than those of acetonitrile-ligated catalysts, and the carbonyl catalyst with the smaller substituents (Me) reached TONHCOOH =5634 (24 h), which is the best performance among the experiments.

Controlling the Depolymerization of Paraformaldehyde with Pd-Phosphine Complexes.

Paraformaldehyde is an easy-to-handle chemical for the in situ generation of formaldehyde and is, therefore, often used in chemistry, structural biology, or medicine. We have investigated the depolymerization process of paraformaldehyde at different temperatures for the application as C1 surrogate in "CO-free" carbonylation reactions using in situ Raman spectroscopy. Rather surprisingly, it was found that small amounts of commonly applied carbonylation catalysts slow down the depolymerization process significantly. By applying 1 H, 17 O, and 31 P NMR spectroscopy coupled with DFT calculations the inhibition process could be assigned to an electron-withdrawing coordination behavior of the Pd complex at the chain end of the paraformaldehyde chain. This inhibition process can be controlled by the utilized phosphine ligand.

Highly dispersed Cu supported on mesoporous Al‐KIT‐6 for oxidative carbonylation of methanol to dimethyl carbonate

Microporous NaY zeolite is a common support of Cu catalysts for oxidative carbonylation of methanol, but the dispersion of Cu species on NaY is usually subjected to its micropore size. Here, ordered mesoporous KIT‐6 was employed as the support for Cu catalyst and Al was incorporated into its framework to increase the surface acidity, which eventually improves the surface exchange capacity and Cu dispersion. The evolution of the state of Cu species on KIT‐6 was analyzed combined with control of Cu loading. The physicochemical properties of the supports and corresponding catalysts were characterized by N2 adsorption–desorption, X‐ray diffraction, ammonia temperature programmed desorption, Fourier transform infrared spectra, transmission electron microscopy, hydrogen temperature programmed reduction, and X‐ray photoelectron spectroscopy. It was found that mesoporous KIT‐6 showed better Cu dispersion than microporous NaY zeolite. Agglomerated CuO, dispersed CuO, and Cu2+ are the major Cu species observed on the catalyst surface. The increased surface acidic sites of KIT‐6 by Al incorporation promoted the formation of Cu2+ and dispersion of CuO. With the increase in Cu loading, the Cu2+ content in the catalyst was decreased gradually along with increase in the bulk CuO. It was speculated that some exchanged Cu2+ could be transformed into highly dispersed CuO and even bulk CuO after calcination at a high Cu loading. Combined with the catalyst evaluation results, it was deduced that highly dispersed Cu2+ and CuO particles play significant roles in catalytic activity. The catalyst Cu/Al‐K‐10 achieved the highest space time yield of dimethyl carbonate of 135.4 mg/(g·h), which is 2.7 times the Cu/K‐10 owing to its more dispersed Cu species. This laid the basis for preparing highly dispersed Cu species on mesoporous silica supports.

Direct Heterogenization of Salphen Coordination Complexes to Porous Organic Polymers: Catalysts for Ring-Expansion Carbonylation of Epoxides

Salen and salphens are important ligands in coordination chemistry due to their ability to form various metal complexes that can be used for a variety of organic transformations. However, salen/salphen complexes are difficult to separate from the reaction mixture, thereby limiting their application to homogeneous systems. Accordingly, considerable effort has been spent to heterogenize the metallosalen/salphen complexes; however, this has resulted in compromised activities and selectivities. Direct heterogenization of metallosalens to form porous organic polymers (POPs) shows promise for heterogeneous catalysis, because it would allow easy separation while retaining catalytic function. Thus, a facile synthetic strategy for preparing metallosalen/salphen-based porous organic polymers through direct molecular knitting using a Friedel-Crafts reaction is presented herein for the first time. As representative candidates, salphenM(III)Cl (M = Al3+ and Cr3+) complexes are knitted by covalent cross-linking using this facile, scalable, one-pot method to synthesize highly POPs in high yields. When incorporated with [Co(CO)4]- anions, the resulting heterogeneous Lewis acidic metal (Al3+ and Cr3+) POPs exhibit propylene oxide ring-expansion carbonylation activity on par with those of their homogeneous counterparts.

Insights into the Pyridine-Modified MOR Zeolite Catalysts for DME Carbonylation

Pyridine-modified mordenite (MOR) zeolite catalysts have attracted great attention in recent years due to their unique shape selectivity within eight-membered ring (8-MR) side pockets for dimethyl ...

Carbon nanotube-supported Cu-based catalysts for oxidative carbonylation of methanol to methyl carbonate: effect of nanotube pore size

The inner diameter of CNTs significantly affected the location, dispersion, autoreduction and stability of Cu species and thus the catalytic activity and stability for oxidative carbonylation of methanol to dimethyl carbonate.

Sterically hindered Re- and Mn-CO2 reduction catalysts for solar energy conversion.

Novel molecular Re and Mn tricarbonyl complexes bearing a bipyridyl ligand functionalised with sterically hindering substituents in the 6,6'-position, [M(HPEAB)(CO)3(X)] (M/X = Re/Cl, Mn/Br; HPEAB = 6,6'-{N-(4-hexylphenyl)-N(ethyl)-amido}-2,2'-bipyridine) have been synthesised, fully characterised including by single crystal X-ray crystallography, and their propensity to act as catalysts for the electrochemical and photochemical reduction of CO2 has been established. Controlled potential electrolysis showed that the catalysts are effective for electrochemical CO2-reduction, yielding CO as the product (in MeCN for the Re-complex, in 95 : 5 (v/v) MeCN : H2O mixture for the Mn-complex). The recyclability of the catalysts was demonstrated through replenishment of CO2 within solution. The novel catalysts had similar reduction potentials to previously reported complexes of similar structure, and results of the foot-of-the-wave analysis showed comparable maximum turnover rates, too. The tentative mechanisms for activation of the pre-catalysts were proposed on the basis of IR-spectroelectrochemical data aided by DFT calculations. It is shown that the typical dimerisation of the Mn-catalyst was prevented by incorporation of sterically hindering groups, whilst the Re-catalyst undergoes the usual mechanism following chloride ion loss. No photochemical CO2 reduction was observed for the rhenium complex in the presence of a sacrificial donor (triethylamine), which was attributed to the short triplet excited state lifetime (3.6 ns), insufficient for diffusion-controlled electron transfer. Importantly, [Mn(HPEAB)(CO)3Br] can act as a CO2 reduction catalyst when photosensitised by a zinc porphyrin under red light irradiation (λ > 600 nm) in MeCN : H2O (95 : 5); there has been only one reported example of photoactivating Mn-catalysts with porphyrins in this manner. Thus, this work demonstrates the wide utility of sterically protected Re- and Mn-diimine carbonyl catalysts, where the rate and yield of CO-production can be adjusted based on the metal centre and catalytic conditions, with the advantage of suppressing unwanted side-reactions through steric protection of the vacant coordination site.