MOR Catalysts Research Articles

The key role of the second material's OER activity on MOR durability enhancement of the Pt alloys

Pt-based precious metal catalysts are generally regarded as the best catalyst materials for direct methanol fuel cells due to their high inherent methanol oxidation (MOR) activity. However, the commercial application of Pt catalyst is still facing with severe durability problem. The CO formed by the incomplete oxidation of methanol will occupy the Pt active site, hindering the further progress of the MOR reaction and causing the rapid attenuation of the activity. In this work, a MOR durability enhancement strategy that relation to the OER performance of the second materials M (M=Ni, Co, Fe and Cu) is reported. The precise electrochemical test results showed that the MOR durability of Pt-M alloy changes with the second material, which is related to the OER activity of M materials. The smaller the overpotential and tafel slopes of the M material, the better the MOR durability. Via M material screening, the Co element with the lowest OER overpotential among M promoted the Pt-Co alloy material with the highest MOR durability, resulting an excellent durability sustain 7000 times CV cycles with just 0.53 A mg−1Pt mass activity loss. According to the current generally accepted OER and MOR reaction mechanism, the association of MOR durability with OER activity is most likely derived from the same reaction step of M-OH formation, which played a key role on both reaction. This relationship between OER overpotential and MOR durability helps to screen the second material from the perspective of OER activity to improve the MOR durability of Pt catalysts, which is of great significance for the development of Pt-based CO-resistant MOR catalysts.

Synthesis of Hydrocarbons over a Bifunctional Oxide/Zeolite catalyst – A Study on Intermediates

The direct conversion of syngas into hydrocarbons, catalyzed by a combination of metal oxide and acidic zeolite, has garnered increasing attention in the scientific community. The remarkable hydrocarbon selectivity achieved in the OX‐ZEO process is a key factor in this growing interest. This process involves two distinct steps: CO activation over the oxide and subsequent C‐C coupling within the zeolite pores, connected by an unidentified oxygenate intermediate. In this study, we explored three proposed oxygenates as potential intermediates and compared their conversion within the OX‐ZEO process. Using a bifunctional ZnCr2O4/H‐MOR catalyst in a syngas‐fed batch reactor, we found that methanol (MeOH) and dimethyl ether (DME) produced a hydrocarbon distribution similar to syngas conversion. However, the conversion of acetic acid (AcOH) resulted in a notably distinct range of hydrocarbons, including short olefins not detected with other reagents. Our findings suggest that methanol/DME might serve as active intermediates in the OX‐ZEO process over the ZnCr2O4/H‐MOR catalyst. This study provides a deeper insight into the transformation of proposed intermediates, contributing to the identification of the bridging intermediate that links the two catalytic functions.

Insights Into the one‐Step Dimethyl Ether Carbonylation to Ethanol Over Cu/ZnO@Cu‐MOR Core‐Shell Catalysts with Porogen Engagement

AbstractThis study investigates the one‐step ethanol synthesis from dimethyl ether and syngas using the catalysts combining Cu/ZnO oxides and modified Cu‐MOR zeolite. In addition to physically mixed two‐component catalysts, multifunctional catalysts featuring a Cu/ZnO core and modified zeolite (Cu‐MOR and HMOR) shell are also presented. Further, the porogenic agent of dihexadecyldimethylammonium bromide (DHAB) was involved in the synthesis process of the MOR zeolite components of Cu/ZnO@Cu‐MOR and Cu/ZnO/Cu‐MOR catalysts, but not in that of Cu/ZnO@Cu‐MOR° catalyst. A series of characterization measures including XRD, TGA, BET, SEM, TEM and EDS have been systematically studied on the prepared catalysts. Characterizations of the catalyst surface structure and texturing parameters revealed a disturbance in crystallinity upon Cu insertion, facilitating syngas separation and promoting DME carbonylation while preventing undesired CO hydrogenation. The addition of DHAB as a porogen in the synthesis of zeolite shell improved specific surface area and porosity of zeolite shell, and reduced coke deposition, without leaching active metal components, resulting in enhanced reaction properties. Cu/ZnO@Cu‐MOR core‐shell catalyst showed good performance with 28.9 % DME conversion and 43.8 % selectivity for ethanol. The optimized pore structure and enhanced catalytic performance of the modification process validate the effectiveness and efficiency of this strategy.

Isomerization performance of n-hexane in hydrogen atmosphere over the multistage porous composite NixPy-MCM-41/MOR catalyst

With the increasingly strict environmental protection requirements and the continuous improvement for the performance of clean fuel, it is imperative to develop technology for producing high octane gasoline blending components. Alkane isomerization was one of the important ways due to it contain little olefin and aromatic components which are harmful to the environment. In this study, the multistage porous composite NixPy-MCM-41/MOR catalysts were synthesized in the hydrogen atmosphere, the conversion rate and selectivity of n-hexane hydrogen isomerization with different conditions was tested in a fixed bed reactor. The results shown that the loading volume of active components is 4.0 wt%, nickel-phosphorus ratio of 0.5, reaction temperature of 250 °C, reaction pressure 3.0 MPa and volume space velocity is 2.0 h−1 with the hydrogen condition showed good catalytic activity for the n-hexane isomerization. The conversion rate of n-hexane is 73.0 % and the selectivity of 84.0 %, respectively. The isomerization stability of the Ni2P-MCM-41/MOR catalyst was investigated. After the long period test, the catalytic activity of the catalyst could keep good. Based on the study of reaction effect with different test conditions in hydrogen atmosphere, the mechanism of alkane isomerization for Ni2P-MCM-41/MOR catalyst was proposed.

Synthesis of mordenite by solvent-free method and its application in the dimethyl ether carbonylation reaction

Mordenite with different Si/Al ratios were synthesized by solvent-free method and used for dimethyl ether (DME) carbonylation reaction. The influence of Si/Al ratio in the feedstock on the structure, porosity and acid sites were systematically investigated. The characterization results showed that with the increase of Si/Al ratio in the feedstock, part of silicon species fail to enter the skeleton and the specific surface area and pore volume of the samples decreased. The amount of weak acid and medium strong acid decreased alongside with the increasing Si/Al ratio, and the amount of strong acid slightly increased. The Al atoms preferentially enter the strong acid sites in the 8 MR channel during the crystallization process. The high Si/Al ratio sample had more acid sites located in the 8 MR channel, leading to more active sites for carbonylation reaction and higher catalytic performance. Appropriately increasing the Si/Al ratio was beneficial for the improvement of carbonylation reaction activity over the MOR catalyst.

Cu and Zn Bimetallic Co-Modified H-MOR Catalyst for Direct Oxidation of Low-Concentration Methane to Methanol.

The direct oxidation of low-concentration methane to value-added chemicals can not only reduce carbon emission but also provide an alternative production route for fossil fuels. Herein, we proposed a novel catalyst for the direct oxidation of low-concentration methane to methanol via the impregnation method, which selected copper and zinc as co-modifiers to modify the MOR catalyst. The highest methanol yield of 71.35 μmol·gcat-1·h-1 was obtained over a bimetallic Cu0.5Zn0.35-MOR catalyst. The catalyst retained good activity after three cycles of testing experiments, indicating good recyclability. Based on the results of performance tests and characterization studies, it was confirmed that Cu species bound to the zeolite framework were the main active sites for methane oxidation. The introduction of Zn decreased the generation of the octahedrally coordinated extra-framework aluminum, which promoted the dispersion of Cu within the zeolite framework. In other words, more tetrahedrally coordinated FAl-stabilized Cu species were presented in our CuZn-MOR catalyst system in comparison to the monometallic Cu-MOR catalyst. Benefiting from the aforementioned modification, the agglomerative sintering of the metal during the reaction was effectively prevented. This work may provide a feasible guide for the future optimization of Cu-based catalysts designed for the selective oxidation of methane.

Highly Selective Conversion of Carbon Dioxide to Methanol through a Cu−ZnO−Al2O3−ZrO2/Cu−MOR Tandem Catalyst

AbstractMethanol formation from CO2 hydrogenation attracts great attention in view of utilization of carbon resources. However, CO2 transformation to methanol is challenging because of the thermodynamic equilibrium restriction and water‐caused catalyst deactivation. It is desired, therefore, to develop highly active, selective and stable catalysts for CO2 hydrogenation to methanol. Herein, we propose a novel tandem catalyst composed of Cu−ZnO−Al2O3−ZrO2 (CZAZ) and Cu−MOR for highly selective conversion of CO2 to methanol. During CO2 hydrogenation by the CZAZ catalyst, the by‐product methane is continuously transformed to methanol through reaction with water via the Cu−MOR catalyst, thus enhancing CO2 conversion and methanol selectivity. Under mild reaction conditions (200 °C and 3.0 MPa), high CO2 conversion (40.7 %) and methanol selectivity (97.6 %) are achieved, outperforming state‐of‐the‐art CO2 hydrogenation catalysts. Further, water‐caused deactivation of the catalyst through aggregation and densification is suppressed owing to water consumption via methane oxidation to methanol, validating a high CZAZ/Cu−MOR tandem catalyst stability.

The Tunable and Efficient Nanoporous CuAg Alloy Catalysts Toward Methanol Oxidation Reaction Synthesized by Electrochemical Dealloying of Metallic Glassy Precursors.

Three-dimensional (3D) nanoporous CuAg (NPCuAg) alloy catalysts with various Cu/Ag ratios are prepared by electrochemical dealloying of metallic glassy (MG) precursors. All dealloyed samples exhibit homogenous nanoporous structure and element composition distribution. After systematically evaluating their electrocatalytic performance toward MOR, it was found that the catalytic activity of the NPCuAg catalysts is enhanced along with the increase of Cu/Ag ratio, which may be attributed to the more exposed active reaction sites derived from high surface area of nanoporous structure and the optimal synergistic effect. Thus, the NPCu1.75 Ag alloy catalyst presents the best methanol electro-oxidation properties, including a high current density of 397.2 mA cm-2 and good operation stability that retaining 84.5 % catalytic activity even after 7200 s. These results outperform most reported copper-based MOR catalysts in alkaline methanol solution. Considering these advantages, the designed electrodes are expected to be promising catalysts for alkaline DMFCs applications.

Facile preparation of a methanol catalyst with ultra-high voltage efficiency and super-durability: Pt pollution introduction by composite electrodeposition

We innovatively develop a high-performance MOR catalyst with small amounts (3.2 wt%) of Pt by composite electrodeposition using a Pt plate as a counter electrode. The material exhibits ultra-high voltage efficiency and unparalleled stability.

Self-Assembled Nano-Filamentous Zeolite Catalyst to Realize Efficient One-Step Ethanol Synthesis.

The non-petroleum synthesis route of ethanol from syngas (H2 +CO) with methyl acetate (MA) as the core intermediate product has been confirmed as an excellent industrialization route for high purity ethanol production. However, as the central part of this tandem-catalysis path, the carbonylation of dimethyl ether (DME) to MA is limited by the undesirable catalytic activity and stability of zeolite catalysts. Herein, a facile inhibitor-assisted strategy was developed for constructing self-assembled nano-Mordenite (nano-MOR) zeolites without using any expensive or complex template. A nano-filamentous MOR zeolite with only 70 nm crystal diameter was successfully synthesized by selectively controlling the crystal growth orientation with a specific inhibitor. The catalytic performance of self-assembled nano-MOR catalysts was remarkably outstanding in DME carbonylation reaction. The highest Space-Time Yield (STY) of MA was achieved over Nanofilament MOR (NF-MOR), which was significantly improved comparing with that of the traditional Ellipsoid-MOR (ES-MOR) [3780 mmol/(kg ⋅ h) vs. 1368 mmol/(kg ⋅ h)]. One-step ethanol synthesis was realized by combining the MOR catalyst and an innovative self-reduced Cu-ZnO/SiO2 (CZ/SiO2 ) catalyst in a rationally designed dual-bed catalysis system. Adopting the tailor-made NF-MOR&CZ/SiO2 combination, it obtained the highest STY of ethanol, about 4 times of the conventional ES-MOR&CZ combination [1800 mmol/(kg ⋅ h) vs. 476 mmol/(kg ⋅ h)]. The present self-assembled nano-MOR zeolites synthetic strategy opens a new way for the fabrication of high-performance zeolites for practical industrial applications in catalytic conversions of one-carbon (C1) small molecules to high value-added chemicals.

Improved methanol electrooxidation catalyzed by ordered mesoporous Pt-Ru-Ir alloy nanostructures with trace Ir content

Mesoporous nanostructures of Pt alloy with Ru-Ir as trimetallic electrocatalyst exhibits significant performance for direct methanol fuel cell (DMFC). In this study, the ordered mesoporous nanostructure (OMNs) of Pt-Ru-Ir catalyst was prepared through the KIT-6 mesoporous silica template-assisted chemical reduction method. The OMN of Pt-Ru-Ir possesses high Pt utilization and a low Ir content, resulting in promoted MOR kinetics by the bi-functional mechanism of its oxophilic nature. In addition, the oxides of both Ru and Ir further enhanced the electrocatalytic efficiency of Pt by producing more active sites owing to its ordered mesoporous morphology and bifunctional mechanism. Furthermore, the OMNs of Pt0.7Ru0.25Ir0.05 electrocatalyst has a substantial electrochemical surface area (ECSA) of 78.35 m2 g−1 with 1721 mA mg−1 of mass activity, which is comparatively 2-3 times higher than all other catalysts reported here. Notably, the ECSA loss (19.5 %) after 5000 durability cycles was found much lesser than other compositions, Pt/C and Pt0.7Ru0.3 catalyst owing to the synergistic effect between Pt and Ru with a trace amount of Ir, smaller particle size, and unique ordered mesoporous morphology. Another significant factor is the rate of CO poisoning during MOR, which was found to be much lesser than others for the Pt0.7Ru0.25Ir0.05 catalyst (∼0.0047 %) studied by chronoamperometry test. The results indicate that the unique OMNs of Pt-Ru-Ir is an excellent MOR catalyst for DMFC applications.

Low temperature ethanol dehydration performed by MOR catalysts obtained from 2D–3D transformation

The silanol groups present on the surface of lamellar silicates are excellent reaction sites for a varied number of chemical modifications. The conversion of these solids into zeolitic structures has shown to be an interesting synthetic alternative, once avoiding hard templating methods and producing materials with particular characteristics. In this work, a post-synthesis OSDA-free procedure was employed for the 2D–3D transformation of Na-RUB-18 lamellar silicate into mordenite zeolite. The conversion was performed at 140 °C and produced small zeolitic crystals (300–500 nm) after 12 and 24 h of crystallization. The reaction presented 65% yield (mol/mol SiO2), producing materials with a similar Si/Al molar ratio (around 6). The 27Al MAS NMR spectra showed signals related to tetrahedrally coordinated aluminum. The N2 adsorption/desorption isotherms confirmed the solids microporous nature and volume (0.36 and 0.43 cm3 g−1). The number of acidic sites was determined by NH3-TPD (976 and 848 µmol g−1), which also revealed sites with weak and moderate to strong acidity. Finally, the samples’ catalytic activity was evaluated by the ethanol dehydration reaction performed at low temperature (150 °C). The synthesized materials were compared to a commercial sample and all the catalysts showed ethanol conversion around 70%, producing ethene and diethyl ether; the latter being the major product at the employed temperature. Unlike the commercial sample, the synthesized ones did not present any deactivation during the time on stream. This feature was attributed to their low-defect structure and subtle mesoporosity.

Promoting Effect of Copper Loading and Mesoporosity on Cu-MOR in the Carbonylation of Dimethyl Ether to Methyl Acetate

Cu-mordenite (Cu-MOR) catalysts with different copper loadings were prepared, characterized and examined in continuous, gas-flow synthesis of methyl acetate (MA) by dimethyl ether (DME) carbonylation. Improved activity and selectivity were observed for Cu-MOR catalysts with up to 1 wt% Cu and X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and temperature-programmed reduction with hydrogen (H2-TPR) were used to elucidate the state of copper in the catalysts. Moreover, mesoporous MOR catalysts (RHMs) were prepared by mild stepwise recrystallization with X-ray powder diffraction (XRPD) and ammonia temperature-programmed desorption (NH3-TPD) demonstrating the retained MOR structure and the acid property of the catalysts, respectively. The RHM catalysts showed improved lifetime compared to pristine MOR giving a yield up to 78% MA with 93% selectivity after 5 h on stream (GHSV = 6711 h−1). Under identical reaction conditions, 1 wt% Cu-RHM catalysts had an even higher catalytic activity and durability resulting in a MA yield of 90% with 97% selectivity for 7–8 h of operation as well as a lower coke formation.

Selective conversion of methanol to propylene over highly dealuminated mordenite: Al location and crystal morphology effects

The growing consumption of light olefins has stimulated intensive researches on methanol to olefin (MTO) process which possesses great advantages for coal conversion to value-added chemicals in an environmentally benign way. The catalysts commonly used for MTO process faces several challenges such as poor selectivity control, low hydrothermal stability and short lifetime. In the present study, we prepared a series of mordenite zeolites with variable Al contents (Si/Al molar ratios of 51−436) by a sequential dealumination treatment of air-calcination and acid leaching. The textural properties, acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene (MTP) performance was thoroughly investigated. The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway, providing a high propylene selectivity of 63% and propylene/ethylene ratio of > 10. Compared to the low-silica MOR catalysts, highly dealuminated MOR showed much higher stability and longer lifetime, which can be further enhanced via harsh hydrothermal pretreatment. Furthermore, the lifetime was highly related to the crystal size along c-axis. The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8-member ring (MR) side pockets and 12-MR pore channels.

Predicting the Catalytic Activity of Surface Oxidation Reactions by Ionization Energies

Developing a descriptor to understand the reactivity of a catalyst is critical in achieving the rational design of heterogeneous catalysts. Ideally, the descriptor should be simple, predictive, as ...

Catalytic Properties of Microporous Zeolite Catalysts in Synthesis of Isosorbide from Sorbitol by Dehydration

As bisphenol A has been found to cause hormonal disturbances, the natural biomaterial isosorbide is emerging as a substitute. In this study, a method for isosorbide synthesis from sorbitol was proposed by dehydration under high temperature and high pressure reaction. Microporous zeolites and Amberlyst 35 solid acids with various acid strengths and pore characteristics were applied as catalysts. In the synthesis of isosorbide from sorbitol, the acidity of the catalyst was the main factor. MOR and MFI zeolite catalysts with high acid strength and small pore size showed low conversion of sorbitol and low yield of isosorbide. On the other hand, the conversion of sorbitol was high in BEA zeolite with moderate acid strength. Amberlyst 35 solid acid catalysts showed a relatively high conversion of sorbitol, but low yield of isosorbide. The Amberlyst 35 solid acid catalyst without micropores did not show any inhibitory effects on the production of by-products. However, in the BEA zeolite catalyst, which has a relatively large pore structure compared with the MOR and MFI zeolites, the formation of by-products was suppressed in the pores, thereby improving the yield of isosorbide.

Synthesis And Characterization Of CoMo/Mordenite Catalyst For Hydrotreatment Of Lignin Compound Models

AbstractThe synthesis of CoMo/Mordenite (CoMo/MOR) catalysts was conducted using a co-impregnation method at a various Co/Mo ratios. The produced catalysts were then characterized by X-ray diffraction, total acidity analysis, and scanning electron microscopy. The activity of the catalyst in a hydrotreatment reaction was evaluated by applying the catalyst as a reduced-catalyst to the hydrocracking (HC) reaction of anisole molecules. Analysis of the diffraction data using the Le Bail refinement technique showed that the metal phase was successfully impregnated into the MOR. In addition, increasing the metal content resulted in an increase in the acidity of the catalysts and changed the morphology of the catalysts from homogeneous to heterogeneous with larger particle size. According to the data of GCMS, it is known that the catalysts successfully removed methyl group of anisole molecules. Hydrotreatment reaction with the prepared-catalyst produced 4.77% of phenols. It is 122 % higher than the reaction with MOR catalyst.

PtCuNi Tetrahedra Catalysts with Tailored Surfaces for Efficient Alcohol Oxidation.

Direct methanol/ethanol alkaline fuel cells (DMAFCs/DEAFCs) represent an attractive mobile power generation technology. The methanol/ethanol oxidation reaction (MOR/EOR) often requires high-performance yet expensive Pt-based catalysts that may be easily poisoned. Herein, we report the development of PtCuNi tetrahedra electrocatalysts with optimized specific activity and mass activity for MOR and EOR. Our synthetic and structural characterizations show that these PtCuNi tetrahedra have Cu-rich core and PtNi-rich shell with tunable surface composition. Electrocatalytic studies demonstrate that Pt56Cu28Ni16 exhibits exceptional MOR and EOR specific activities of 14.0 ± 1.0 mA/cm2 and 11.2 ± 1.0 mA/cm2, respectively and record high mass activity of 7.0 ± 0.5 A/mgPt and 5.6 ± 0.6 A/mgPt, comparing favorably with the best MOR or EOR Pt alloy-based catalysts reported to date. Furthermore, we show that the unique core-shell tetrahedra configuration can also lead to considerably improved durability.

Methods for reducing flue gas emissions from fluid catalytic cracking unit regenerators

The dimethyl ether (DME) carbonylation reaction over mordenite is greatly affected by the mass transfer process. In this research, hierarchical mordenite catalysts were synthesized and characterized to investigate the influence of mesopores on the structure, mass transfer and catalytic performance. The results show that the medium-strong acid sites decrease while strong acid sites increase over the hierarchical samples. The introduced mesopores can significantly improve the mass transfer efficiency and the carbonylation performances are markedly improved on the hierarchical samples. In addition, the polymerization degree of coke deposition on the deactivated samples decreases although the coke amount increases. Excessive usage of mesopore templates can damage the structure of the MOR catalysts, thus leading to the loss of acid sites and the decrease in catalytic performance.

Dual role of hemin in Pt nanoparticle deposition on carbon nanotubes for methanol electro-oxidation and oxygen reduction

This paper presents a novel and simple non-covalent method to synthesize a double-cladding coaxial structured hybrid by depositing Pt nanoparticles on hemin-coated multi-walled carbon nanotubes (MWCNTs). The Pt nanoparticles cooperated with hemin can be used for methanol electro-oxidation and oxygen reduction. Transmission electron microscopy showed that the Pt nanoparticles were uniformly dispersed on the hemin-coated MWCNTs with a small particle size and a narrow particle size distribution. Cyclic voltammetry tests revealed that the as-prepared Pt/hemin-coated MWCNT electrocatalysts exhibited higher electrochemical surface area (67.46 m2/g) and current density (425.0 mA mg−1) for methanol oxidation than Pt/MWCNTs. These improvements can be attributed to the dual role of hemin in the dispersion of Pt nanoparticles on functionalized MWCNTs and the synergy of catalysis in methanol electro-oxidation and oxygen reduction. It's the first time to report the functionalization of CNTs with catalytic hemin as the binder between CNTs and the metal nanoparticles of MOR or ORR catalyst.