Molybdenum Phosphide Catalysts Research Articles

Improving catalytic activity of MoP for CO2 reforming of methane via ZrO2 modification

Molybdenum phosphide (MoP) has attracted increasing attention as a novel catalytic material for CO2 reforming of methane in virtue of superior coke resistance, but its catalytic reactivity is still relatively low. This work for the first time improved the reforming activity of MoP via ZrO2 modification. The Zr0.01MoP catalyst with Zr/Mo molar ratio of 0.01 possessed much higher activity than bare MoP at 800–900 °C. Structural characterizations revealed that the introduction of ZrO2 would decrease the particle size, modify the electronic structure and change the reducibility property of MoP, which may function together to deliver the higher activity.

ZIF-8 induced N, P double doped porous molybdenum phosphide hydrogen evolution catalyst

Molybdenum based phosphides have gradually become the investigation frontier of hydrogen evolution catalysts due to the platinum like electronic structure. In this paper, N, P double-doped graphite carbon layers wrapped with MoP nanoparticles (P–MoP@NPC), is directly compounded by one-step high-temperature carboning PMo12-APP@ZIF-8 precursor. P–MoP@NPC possesses splendid hydrogen production reactive, in two kinds of electrolytes, when the overpotentials of P–MoP@NPC are 132 mV and 161 mV, the slope of current density reaching 10 mA cm−2, Tafel slope are 67 and 79 mV dec−1, respectively. In the bargain, P–MoP@NPC displays satisfactory durability in acid and alkaline mediums and can continue to work for more than 24 h. The wonderful hydrogen production ability of P–MoP@NPC is ascribed to the synergistic effect of MoP nanoparticles, hierarchical porous structure as well as N, P double-doped carbon layers. The confinement effect of ZIF-8 makes most of the synthesized MoP nanoparticles evenly distributed. The hierarchical porous structure caused by the volatilization of Zn atoms with high temperature can expose more active centers. The N, P double-doped graphitic carbon layers not only protect the catalyst but also adjust the electronic structure of MoP, promoting the hydrogen production capacity. This work may provide a general way to study molybdenum phosphide catalysts synthesized by APP as a green phosphorus source for energy conversion.

One‐Step Synthesis of Air‐Stable Sulfur‐Doped Molybdenum Phosphide Catalyst

AbstractTransition‐metal phosphides prepared from temperature‐programmed reduction (TPR) are generally known to be unstable and prone to surface structure decomposition upon exposure to air. In this work, air‐stable molybdenum phosphide (MoP) was prepared using TPR modified by sulfur. This catalyst was exposed to ambient atmosphere for up to 150 days and still maintained its surface and bulk structures as the fresh sample derived from in situ reduction. The metal phosphosulfide phase generated during TPR not only contributes to the solid structural properties but also exhibits superior catalytic activity in various hydrofining reactions compared to traditional MoP catalysts. Additionally, this preparation strategy was used to synthesize other sulfur‐doped metal phosphides, such as CoP and Cu3P. Both of these catalysts exhibited excellent air‐stability.

Electronic Phosphide–Support Interactions in Carbon-Supported Molybdenum Phosphide Catalysts Derived from Metal–Organic Frameworks

Electronic Phosphide–Support Interactions in Carbon-Supported Molybdenum Phosphide Catalysts Derived from Metal–Organic Frameworks

Insights into Correlations among the Hydrodesulfurization, Hydrodenitrogenation, and Hydrogen Evolution Reactions over Molybdenum Phosphide Catalysts Modified by Cerium Oxide

Insights into Correlations among the Hydrodesulfurization, Hydrodenitrogenation, and Hydrogen Evolution Reactions over Molybdenum Phosphide Catalysts Modified by Cerium Oxide

In Situ Generated Dispersed Catalysts Based on Molybdenum and Tungsten Phosphides in Hydroprocessing of Guaiacol

Amorphous catalysts based on molybdenum and tungsten phosphides were prepared in situ from oil-soluble precursors such as triphenylphosphine and carbonyls of the corresponding metals during hydrodeoxygenation of guaiacol. These catalysts were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy. After 6 h of reaction at 320–380°C and an initial hydrogen pressure of 5 MPa, the guaiacol conversion amounted to 89–91% in the presence of the molybdenum phosphide catalyst and 80–86% with tungsten phosphide. The selectivity towards phenol as the main reaction product reached as high as 80% in the presence of molybdenum phosphide (360°C, 6 h) and 78% in the tungsten phosphide case (340°C, 1 h). In the presence of both catalytic systems, the reaction products also contained anisole, cresols, and toluene.

CO2 Conversion via Reverse Water Gas Shift Reaction Using Fully Selective Mo-P Multicomponent Catalysts.

The reverse water gas shift reaction (RWGS) has attracted much attention as a potential means to widespread utilization of CO2 through the production of synthesis gas. However, for commercial implementation of RWGS at the scales needed to replace fossil feedstocks with CO2, new catalysts must be developed using earth abundant materials, and these catalysts must suppress the competing methanation reaction completely while maintaining stable performance at elevated temperatures and high conversions producing large quantities of water. Herein we identify molybdenum phosphide (MoP) as a nonprecious metal catalyst that satisfies these requirements. Supported MoP catalysts completely suppress methanation while undergoing minimal deactivation, opening up possibilities for their use in CO2 utilization.

In Situ Studies of the Formation of MoP Catalysts and Their Structure under Reaction Conditions for Higher Alcohol Synthesis: The Role of Promoters and Mesoporous Supports

Three formulations of a molybdenum phosphide (MoP) catalyst system were characterized for the higher alcohol synthesis (HAS) reaction using in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), monitoring the chemical phase evolution during activation and under reaction conditions. The in situ study herein provides important insights into the effect of the support and of K that lead to high performance in HAS for K-promoted MoP supported on carbon, as evidenced by previous studies (ethanol selectivity: 29%; conversion: 5%). During the activation process, XAS shows that the carbon-supported samples reduce and reach a highly crystalline state at a lower temperature than the SBA-15-supported sample, indicating a substantial difference in catalyst activation. After activation, the samples are introduced to relevant reaction conditions resulting in spectra fairly similar to one another. XRD results corroborate the difference in the degree of crystallinity of these samples, in alignment with the XAS, and reveal the formation of crystalline potassium pyrophosphate (K4P2O7) during the activation period of the K-promoted samples. This K4P2O7 phase remains present under reaction conditions. Taken together, these results provide insights into the roles played by the carbon support and K promotion, connecting activity to electronic and crystal structure.

Influence of NiMoP phase on hydrodeoxygenation pathways of jatropha oil

This work investigates the conversion pathway of jatropha oil to C16 + C18 by a one-pot method regulated by different moles of phosphorus and supports. Preferential direct deoxygenation is of interest for the carbon atom economy. Herein, SAPO-11, ZSM-5, and Zr-SBA-15 as supports, a series of nickel molybdenum phosphide catalysts were prepared, characterized, and used to hydrodeoxygenation (HDO) of jatropha oil in an autoclave. Our results showed that different supports affect the formation of the active phase of nickel molybdenum phosphide and its acid sites, thus affecting the catalytic performance, resulting in different HDO pathway ratios. The HDO pathway ratios of different n(Ni–Mo)/n(P) catalysts on the same support differed. Compared with the NiMo catalysts, the NiMoP2/Zr-SBA-15 catalyst showed the most remarkable HDO performance, with C15 + C17/C16 + C18 decreasing from 6.95 to 2.24. The presence of P in the catalyst promotes direct deoxygenation, while inhibiting decarboxylation and decarbonylation. In addition, the NiMoP phase exhibited excellent catalytic activity, with more than 90% deoxidization. Refined oil contains high levels of jet fuel components, with C8–C16 alkanes account for more than 50% and naphthenes reaching more than 20%. The catalysts were tested at 360 °C, 30 bar, and 4 h, and results showed that the NiMoP phase plays an important role in inhibiting coke deposition on the catalyst.

Boosting Hydrogen Evolution Reaction via Electronic Coupling of Cerium Phosphate with Molybdenum Phosphide Nanobelts.

Molybdenum phosphide (MoP) is regarded as one of the most promising alternatives to noble-metal based electrocatalysts for efficient hydrogen evolution reaction (HER) due to its similar d-band electronic structure to noble metals and tunable features associated with phase and composition. However, it still remains a great challenge to construct MoP electrocatalysts with abundant active sites that possess ideal H binding strength to promote catalytic performance. In this work, it is found that by anchoring a rare earth compound, cerium phosphate (CePO4 ) on MoP (CePO4 /MoP), the stabilized Ce3+ in CePO4 can significantly boost the formation of oxygen vacancies in ceria (CeO2 ) in situ formed on CePO4 surface during HER, which effectively regulates the d-band electronic density-of-states of MoP, increases the numbers of active sites, and promotes the vectorial electron transfer, therefore greatly enhancing the HER performance of MoP. The optimized CePO4 /MoP/carbon cloth (CC) electrocatalyst exhibits a significantly improved HER performance with an overpotential of 48 mV at 10 mA cm-2 and a Tafel slope of 38 mV dec-1 , about two times better than the HER performance of MoP catalyst without CePO4 (with an overpotential >80 mV dec-1 at 10 mA cm-2 ), very close to commercial Pt/C catalyst.

Phytic acid-derived fabrication of ultra-small MoP nanoparticles for efficient CO methanation: Effects of P/Mo ratios

Molybdenum phosphide (MoP) catalyst has been widely applied in hydrogenation reactions, while the preparation of unsupported MoP catalysts with ultra-small size and large specific surface area (SBET) is still challenging. Herein, we have provided a facile method for preparing a series of MoP-x (x = P/Mo ratios ranging from 1 to 5) catalysts by pyrolyzing phytic acid (PA)-derived Mo complexes in a H2 atmosphere. The physicochemical properties and the catalytic activity of MoP catalysts were investigated. The results showed that the obtained MoP-5 catalyst had the largest SBET and exhibited ultra-small nanoparticle diameter of 3.6 nm, which ascribed to the chelation of PA and the confinement of deposited products. As the content of PA increased, the synthetic mechanism of MoP was also affected, which led to the difference in the valence of surface Mo species. The characterization results further confirmed that Moδ+ sites in MoP catalysts are active sites for methanation reaction and its content on the surface of MoP-x catalysts determines the catalytic activity.

Development of Molybdenum Phosphide Catalysts for Higher Alcohol Synthesis from Syngas by Exploiting Support and Promoter Effects

Molybdenum phosphide (MoP) catalysts have recently attracted attention due to their robust methanol synthesis activity from CO/CO2. Synthesis strategies are used to steer MoP selectivity toward higher alcohols by investigating the promotion effects of alkali (K) and CO‐dissociating (Co, Ni) and non‐CO‐dissociating (Pd) metals. A systematic study with transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy (XAS) showed that critical parameters governing the activity of MoP catalysts are P/Mo ratio and K loading, both facilitating MoP formation. The kinetic studies of mesoporous silica‐supported MoP catalysts show a twofold role of K, which also acts as an electronic promoter by increasing the total alcohol selectivity and chain length. Palladium (Pd) increases CO conversion, but decreases alcohol chain length. The use of mesoporous carbon (MC) support has the most significant effect on catalyst performance and yields a KMoP/MC catalyst that ranks among the state‐of‐the‐art in terms of selectivity to higher alcohols.

A comparative study of molybdenum phosphide catalyst for partial oxidation and dry reforming of methane

Abstract Molybdenum phosphide (MoP) was firstly used as a catalyst for partial oxidation of methane (POM) and its catalytic performance for POM was compared with that for dry reforming of methane (DRM). It was found that the MoP phase was the dominant active site in POM and DRM reactions, and the activity would gradually decrease when more and more MoP was converted to Mo2C phase (non-dominant active site) and then rapid deactivation would occur due to bulk oxidation of catalyst. The redox type mechanism over MoP catalyst was vitally important to keep its structure reasonably well during methane reforming reactions. The MoP catalyst revealed a higher catalytic stability in POM than in DRM, attributing to the higher H2 yield obtained in POM, which can promote and maintain the redox cycle of catalyst.

A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2

AbstractMethanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2/H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2. We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2/H2 feeds.

A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2.

Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2 /H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2 . We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2 /H2 feeds.

Oxygen-incorporated defect-rich MoP for highly efficient hydrogen production in both acidic and alkaline media

Molybdenum phosphide (MoP) has attracted a lot of attentions as a potential electrocatalyst for the hydrogen evolution reaction (HER). Although great efforts have been made to improve the HER activity of MoP, the rational design of MoP catalysts with either more active sites or higher conductivity is still challenging. Herein, a defect-rich structure (DR-MoP) is synthesized via a novel and facile low-temperature calcination strategy. Moreover, the DR-MoP is also proved to be incorporated with oxygen. The defect-rich structures could provide more active sites, and the incorporation of oxygen could further enhance the intrinsic conductivity. Thus, the DR-MoP catalyst shows outstanding HER activity and stability in both acidic and alkaline media, making it a good alternative to replace the precious-metal catalysts. Besides, the formation mechanism of DR-MoP has been discussed by controlling different annealing temperatures. This work paves a novel and effective way for improving the HER performance of transition metal phosphides by defect engineering.

Surface engineering-modulated porous N-doped rod-like molybdenum phosphide catalysts: towards high activity and stability for hydrogen evolution reaction over a wide pH range.

Electrochemical water splitting is an economic, green and sustainable route to produce hydrogen through the hydrogen evolution reaction (HER). Nowadays, noble metal-free phosphides have been widely used as catalysts in the HER, showing potential applications for both renewable energy production and environmental remediation. Nevertheless, developing surface self-doped MoP electrocatalysts with high HER performances in a wide pH range still remains a challenge. In this work, a novel synthesis strategy was developed to fabricate porous one-dimensional (1D) nitrogen-doped molybdenum phosphide (N-MoP) nanorods. The prepared N-MoP-800 catalyst exhibits a low onset potential of 65 mV and low Tafel slope of 58.66 mV dec−1 in 0.5 M H2SO4, which is almost 2 times higher than that of the pristine MoP nanorod anode. Furthermore, the N-MoP materials show long-term durability for 12 h in a wide pH range. The synergistic effects of pyridinic N and N doping in MoP are responsible for the high catalytic activity of N-MoP under acidic conditions, while the N-Mo component plays a key role in enhancing the HER activity of N-MoP. These interesting findings are helpful for the rational design of highly active HER catalysts. More importantly, this study provides a new strategy to synthesize highly active catalysts with low costs for clean energy conversion.

Enhanced hydrogen evolution from the MoP/C hybrid by the modification of Ketjen Black

It is still a great challenge to find highly efficient non-Pt catalysts with good stability for the hydrogen evolution reaction (HER). The molybdenum phosphide (MoP)-based catalysts have been identified as promising candidates to replace noble Pt, but the further improvement of these catalysts is still strongly demanded. Herein, a simple strategy to enhance the HER activity of the MoP catalyst has been proposed, in which a novel MoP/C hybrid is prepared by a facile temperature-programmed reduction method with the modification of Ketjen Black, exhibiting superior HER activity with a smaller Tafel slope of 54 mV dec−1 and a larger current density of 151 mA cm−2 at −400 mV, about 34 times larger than that of the pure MoP catalyst. Moreover, a possible improvement mechanism was also stated.

Effect of surface composition on the catalytic performance of molybdenum phosphide catalysts in the hydrogenation of acetonitrile

A series of molybdenum phosphide catalysts with initial Mo/P ratios varying in a narrow range of 0.90–1.10 was prepared by temperature-programmed reaction; characterized by X-ray diffraction, BET, elemental analysis, X-ray photoelectron spectroscopy, and CO chemisorption measurements; and tested for the hydrogenation of acetonitrile at different pressures (0.1–1.0 MPa) and temperatures (473–513 K). The catalysts exhibited attractive catalytic activity, especially at a H 2 pressure above 0.2 MPa. The surface composition of the MoP catalysts could be fine-tuned by the initial Mo/P ratio, which consequently led to different surface properties (e.g., CO uptakes) and catalytic behaviors. Catalysts with high initial Mo amount gave high selectivity to the primary amine, ethylamine, whereas those with high initial P amount created more condensed amines, diethylamine and triethylamine.

Influence of reduction temperature and metal loading on the performance of molybdenum phosphide catalysts for dibenzothiophene hydrodesulfurization

Two series of alumina-supported molybdenum phosphide (MoP) catalysts with low and high metal loadings were prepared by temperature-programmed reduction of the oxidic catalyst precursors in hydrogen to different temperatures (823, 923, 1023 and 1123 K, respectively). Effects of reduction temperature and metal loading on the surface distribution and the type of species formed were studied by TPR, SBET, XRD, HRTEM, 31P NMR, 27Al NMR and in the reaction of dibenzothiophene (DBT) hydrodesulfurization (HDS) performed in a flow reactor at 553 K and total hydrogen pressure of 3.4 MPa. HRTEM and 31P NMR confirmed formation of MoP phase on all catalysts. The 9.9 wt% Mo catalyst activated at lowest reduction temperature (823 K) was found to be most active among the catalysts studied. The presence of a low amount of Mo0 species on the surface of this catalyst does not appear to be a drawback for the catalytic activity. The increase in both metal loading (from 9.9 to 15 wt% Mo and from 3.2 to 4.8 wt% P) and reduction temperature (from 823 to 1123 K) was found to be detrimental for HDS activity due to sintering of active phase, and also to decrease in specific area and formation of phosphate species.