Production of carbon nanotubes from plastic wastes and application in battery additives

Carbon nanotubes (CNTs) were produced from two plastic waste feedstocks, a polypropylene (PP)-dominated mask and a solid recovered fuel (SRF) with a high content of non-recyclable mixed plastics, using a pyrolysis-chemical vapor deposition (CVD) process. FeMo/MgO and CoMo/MgO catalysts were used for CNT growth using pyrolysis gases containing various hydrocarbons. It was found that CoMo/MgO produced selective and small-walled CNTs, while FeMo/MgO produced high-yield multi-walled CNTs. The CNTs produced from the mask feedstock exhibited higher yield, diameter, and purity compared to those produced from the SRF feedstock. The resulting CNTs were tested as conductive additives in the cathode of a lithium-ion battery (LIB). Electrochemical measurements demonstrated that CNTs produced with FeMo/MgO outperformed commercially available carbon black. This study presents a novel approach for plastic waste utilization, where CNTs produced from plastic waste can be utilized as effective conductive additives for LIB cathodes

Modified Metal-Organic Frameworks as Efficient Catalysts for Lignocellulosic Biomass Conversion

Biomass, a promising replacement for fossil fuels, can be used to produce eco-friendly liquid fuels and chemicals. Various studies are investigating catalysts for lignocellulosic biomass conversion to valuable chemicals and fuels. Metal-organic frameworks (MOFs) are important catalysts because of their well-ordered porous structures and large surface areas. Although MOFs can be applied directly, four modification strategies can be used to alter their catalytic properties and improve catalytic performance. In the first strategy, coordinatively unsaturated sites are created by changing the bonding state of the metal node. In the second approach, organic linkers with additional functional groups or active elements are used. In the third strategy, MOFs and other active elements are combined. In the final approach, MOFs are carbonized to produce carbon-supported metal catalysts. We review the applications of modified MOFs for the catalytic conversion of biomass derivatives and discuss the factors that contribute to their improved catalytic performance

Coke resistant NiCo/CeO2 catalysts for dry reforming of methane derived from core@shell Ni@Co nanoparticles

Core@shell Ni@Co and bimetallic alloyed Ni-Co nanoparticles with controlled Co/Ni compositions were prepared and supported on CeO2 to investigate their performance in catalytic dry reforming of methane (DRM) and occurrence of sintering and coking. Increasing the Co/Ni ratio significantly reduced coke deposition while maintaining catalytic activity for DRM. However, a Co/Ni ratio > 1 caused a rapid decrease in activity. The Ni@Co-1/CeO2 catalyst exhibited the highest CH4 and CO2 conversions, with long-term stability during DRM at 800 ? for 100 h. The initial core@shell structure of the Ni@Co-1/CeO2 catalyst transformed to a homogeneous alloy after DRM at 800 C for 10 h, losing its Co shell. However, the bimetallic alloyed Ni-Co-1/CeO2 catalyst transformed into a non-uniform alloy rich in Co on the surface after DRM for 10 h. As the elemental distribution of the NPs becomes more homogeneous, Ni-Co-1/CeO2 exhibit similar catalytic activity to Ni@Co-1/CeO2 after 50 h. The oxygen vacancies on the CeO2 surface provided oxygen atoms to the Ni surface, removing carbon species deposited and releasing CO. Therefore, Ni@Co-1/CeO2 catalyst provides excellent catalytic activity and stability due to the rapid formation of a homogenous alloy and the synergistic effect of Co and CeO2

A-site effects of titanate-perovskite (ATiO3)-based catalysts on dehydrogenation of N-heterocyclic molecules

Dehydrogenation reactions in liquid organic hydrogen carrier (LOHC) systems present significant challenges, particularly when aiming for low-temperature operations while ensuring that no hydrogen remains in the sub-strate molecules. Enhancing catalytic performance requires modifying the adsorption behavior of the reactants and products during dehydrogenation. Perovskites have emerged as promising catalyst supports because of their ability to modify the surface chemical properties by manipulating the cations present at the A-and B-sites. This study investigated the effects of A-site cations (Ca, Sr, and Ba) in titanate-type perovskite (ATiO3)-a proto-typical perovskite-on the dehydrogenation activity in LOHC systems. Remarkably, Pd/SrTiO3 exhibited outstanding performance by completely converting octahydro-N-methylindole to N-methylindole and releasing 5.76 wt% hydrogen over 8 h. Additionally, it dehydrogenated dodecahydro-N-ethylcarbazole to N-ethylcarbazole with a hydrogen release of 5.70 wt%. Furthermore, the catalyst demonstrated a stable performance after recy-cling tests for three times without degradation or loss of activity. The chemical state of the catalyst surface was characterized through X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and chemi-sorption using NH3, CO2, and H2. The results revealed that the exceptional dehydrogenation activity of Pd/ SrTiO3 is due to the presence of suitable surface oxygen vacancies and abundant acid-base sites

Al2O3-Coated Ni/CeO2 nanoparticles as coke-resistant catalyst for dry reforming of methane

Nickel is considered an economically feasible catalyst for the dry reforming of methane (DRM) owing to its high activity. Because the highly endothermic DRM requires a high reaction temperature to activate both CH4 and CO2, deactivation of the Ni catalyst may be induced by sintering and carbon coking. To mitigate catalyst deactivation, Ni/CeO2 catalysts composed of monodisperse Ni nanoparticles supported on CeO2 nanorods are designed and coated with Al2O3 layers by atomic layer deposition (ALD). The performance of the catalyst in DRM and amount of carbon deposited are correlated with the thickness of the Al2O3 layer in the Ni/CeO2/Al2O3 catalysts. As the number of ALD cycles increases from 1 to 10, the conversion of CO2 and CH4 at 700 and 800 degrees C decreases, but the Ni/CeO2/Al2O3 catalysts remain coke-free as thermogravimetric analysis shows no weight loss up to 800 degrees C. The Al2O3 layer generated by ALD curtails the coking substantially, but the weakly metallic character of Ni and blocking of Ni sites by the Al2O3 layer are the major factors contributing to decreasing the catalytic conversion. The ALD technique provides an efficient way to fabricate atomically controlled oxide layers for improving the stability of catalysts against coke deposition and sintering

Influence of the Pt size and CeO2 morphology at the Pt-CeO2 interface in CO oxidation

Understanding the inherent catalytic nature of the interface between metal nanoparticles (NPs) and oxide supports enables the rational design of metal-support interactions for high catalytic performance. Electronic interactions at the metal-oxide interface create active interfacial sites that produce distinctive catalytic functions. However, because the overall catalytic properties of the interface are influenced by several complex structural factors, it is difficult to express the catalytic activity induced by the interfacial site through a simple descriptor. Based on a combinatorial study of density functional theory calculations and catalytic experiments, we focus on two structural design factors of metal NP-supported oxide catalysts: the size of Pt NPs and the morphology of the CeO2 support. Pt NPs with sizes of 1, 2, and 3 nm were supported on the surface of CeO2-cubic ({100} facet) and -octahedral ({111} facet) nanocrystals. During catalytic CO oxidation, the activity of the Pt/CeO2-cube was higher than that of the Pt/CeO2-octahedron, regardless of the size of the NPs. Although 1 nm Pt NPs donate a similar number of electrons per Pt atom to CeO2-cubes and CeO2-octahedra, the inherently low oxygen vacancy formation energy of the CeO2(100) surface leads to the higher catalytic activity of the Pt-CeO2-cube interface. However, the intrinsic catalytic activity of the interface between Pt NPs and two CeO2 nanocrystals converges as the size of Pt NPs increases. Because large Pt NPs interact more strongly with CeO2(100) than CeO2(111), the positive effect of the low vacancy formation energy of CeO2(100) is compensated by the strengthened Pt-O interaction. This study elucidates how the interfaces formed between the shape-controlled CeO2 and the size-controlled Pt NPs affect the resultant catalytic activity

Reversible Pd Catalysts Supported on Hierarchical Titanate Nanosheets for an <i>N</i>-Methylindole-Based Liquid Organic Hydrogen Carrier

Reversible hydrogenation and dehydrogenation processes were investigated in a liquid organic hydrogen carrier (LOHC) system by employing a single-catalyst approach. Key hydrogen-involved catalytic behaviors, including adsorption and migration, play crucial roles in reactivity. To facilitate these behaviors at the active sites on the catalyst surface during the LOHC process, a defective metal oxide support was utilized. Herein, a Pd catalyst was prepared by using hierarchical titanate nanosheets (HTN) synthesized via solvothermal synthesis. Compared to commercial TiO2 and hierarchical TiO2 (HT), which was synthesized by the calcination of HTN, HTN exhibited a higher density of acidic sites and oxygen vacancies. Density functional theory calculations confirmed that hydrogen spillover occurred more readily on the defective HTN surface than on the TiO2 (101) surface. The Pd/HTN catalyst demonstrated superior catalytic activity for both the hydrogenation and dehydrogenation reactions in the N-methylindole-based LOHC system. The hydrogen uptake of Pd/HTN catalyst (4.73 wt %) was 3 times higher than that of other Pd catalysts (similar to 1.57 wt %). The single Pd/HTN catalyst successfully accomplished reversible hydrogen storage and release within the LOHC system in one reactor

Upcycling of plastic waste into carbon nanotubes as efficient battery additives

Carbon nanotubes (CNTs) were produced from waste face masks and non-recyclable mixed plastic waste via pyrolysis-chemical vapor deposition (CVD). The yield and properties of the prepared CNTs depended on the feedstock and catalyst used. CoMo/MgO and FeMo/MgO were proven suitable catalysts for producing few-walled and multi-walled CNTs, respectively, regardless of the feedstock. Both mask waste and the FeMo/MgO catalyst led to excellent carbon yield (516.7 wt%) and CNT purity (97.9 wt%). The resulting CNTs were mixed with LiNi0.8Co0.1Mn0.1O2 (NCM811) active material and poly(vinylidene fluoride) binder to fabricate cathodes. Electrochemical measurements showed that CNTs grown on the FeMo/MgO catalyst outperformed commercial carbon black and CNTs. C1-C3 hydrocarbons and H2 present in the plastic pyrolysis gas can be directly used for CNT production without gas separation or purification, therefore, the proposed pyrolysis-CVD process is favorable for efficient plastic upcycling and advanced battery applications. Carbon nanotubes (CNTs) were produced from waste face mask and non-recyclable mixed plastic waste via pyrolysis-chemical vapor deposition (CVD)