Density Functional Theory Studyof Water Adsorption on the CoO (100) and CoO (110) Surfaces

The density functional theory (DFT) method was used in this study to determine the chemical and physical properties of Cobalt Oxide (CoO) because it is a reliable, fast and inexpensive technique. This study is designed to determine the electronic properties of CoO bulk and the adsorption energy of the water molecule (H2O) on the CoO surface. CoO crystals used in this study have been optimized by using the GGA-PBE and LDA-CAPZ methods. The study found that calculations using GGA-PBE were closer to the experiment value. Without considering spin orbital interactions, CoO showed a metallic electronic band structure. After considering the spin orbital interaction calculation, each alpha and beta band structures has band gap of 1.55 eV, which is similar to the reported theoretical value. The ground state of CoO is antiferromagnetic base-on alpha and beta band structures. The peak absorption of light representing optical properties at wavelength energy is 351 nm in visible light spectrum (UV) range. The DFT calculation is used to determine the H2O adsorption energy to the surfaces of CoO (100) and CoO (110). H2O adsorption energy on CoO (100) and CoO (110) surfaces is based on eight different configurations, with different H2O adsorption positions on each CoO surface. On the CoO (100) surface, H2O adsorption energy is optimum in Model 5, with a value of 5.123 eV. Meanwhile, the H2O adsorption energy on the CoO (110) surface is optimum in Model 6, with a value of 2.810 eV. Based-on adsorption energy study, it expected that H2O easier to absorb on CoO(110) rather than on CoO(100)

Catalytic decomposition of methane into hydrogen and carbon nanotubes over mesostructured silica nanoparticle-supported nickel catalysts

Hydrogen is an alternative source of renewable energy that can be produced by methane decomposition without any COx formation. In this work, an impregnation method was used to prepare a set of Ni-based catalysts (5% to 50%) supported on mesostructured silica nanoparticles (MSNs) for its application in methane decomposition. The use of MSN as an effective support for nickel in methane decomposition was reported here for the first time. The physical, chemical and structural properties of the catalysts was studied and the results indicated that NiO was the active species in the fresh catalyst that were effectively distributed on the mesoporous surface of MSN. The reduction temperature of Ni/MSN catalysts were shifted to low temperatures with increased loading of nickel. The hydrogen yield increased with the increment of Ni amount in the catalysts. The catalytic activity of the 50% Ni/MSN catalyst showed that this catalyst was highly efficient and stable compared with other catalysts. The catalyst showed the highest hydrogen yield of 68% and remained more or less the same during 360 min of reaction. Approximately 62% of hydrogen yield was observed at the end of reaction. Further analysis on the spent catalysts confirmed that carbon nanotubes was formed over Ni/MSN catalyst with high graphitization degree

Kinetics study of hydrogen adsorption over Pt/MoO3

The rate controlling step and the energy barrier involved in the hydrogen adsorption over Pt/MoO3 were studied. Rates of hydrogen adsorption on Pt/MoO3 were measured at the adsorption temperature range of 323–573 K and at the initial hydrogen pressure of 6.7 kPa. The rate of hydrogen uptake was very high for the initial few minutes for adsorption at and above 473 K, and reached equilibrium within 2 h. At and below 423 K, the hydrogen uptake still continued and did not reach equilibrium after 10 h. The hydrogen uptake exceeded the H/Pt ratio of unity for adsorption at and above 423 K, indicating that hydrogen adsorption involves hydrogen atom spillover and surface diffusion of the spiltover hydrogen atom over the bulk surface of MoO3 followed by formation of HxMoO3. The hydrogen uptake was scarcely appreciable for Pt-free MoO3. The rate controlling step of the hydrogen adsorption on Pt/MoO3 was the surface diffusion of the spiltover hydrogen with the activation energy of 83.1 kJ/mol. The isosteric heats of hydrogen adsorption on Pt/MoO3 were 18.1–16.9 kJ/mol for the hydrogen uptake range 2.4–2.8 × 1019 H-atom/g-cat. Similarities and differences in hydrogen adsorption on Pt/SO42-–ZrO2, Pt/WO3–ZrO2 and Pt/MoO3 catalysts are discussed

Study of the interaction between hydrogen and the MOO3-ZRO2 catalyst

The interaction of molecular hydrogen with the surface of MoO3–ZrO2 was observed using infrared IR and electron spin resonance (ESR) spectroscopy, and the hydrogen adsorption was quantitatively evaluated in the temperature range of 323–573 K. The hydrogen adsorbed IR results confirmed the formation of a new broad band in the range of 3700–3400 cm−1, which corresponds to hydrogen-bonded OH groups. A decrease in the ESR signals indicated the formation of electrons that have been trapped by the electron-deficient metal cations and/or oxygen radicals. The hydrogen adsorbed IR and ESR results suggested that the protons and electrons were formed on the surface of MoO3–ZrO2 from molecular hydrogen enhancing the isomerization of n-heptane. A quantitative study of the hydrogen adsorption showed that the rate of hydrogen uptake was high for the first few minutes at 473 K and above, and the rate reached an equilibrium value within 10 h. At 423 K, different features of the hydrogen adsorption were observed on MoO3–ZrO2, where the hydrogen uptake increased slowly with time and did not reach equilibrium after 10 h. The rate of hydrogen adsorption increased slightly at 373 K and below. Hydrogen adsorption on MoO3–ZrO2 involves two successive steps. The first step involves hydrogen dissociation on a specific site on the MoO3–ZrO2 catalyst to form hydrogen atoms, and the second step involves the surface diffusion of the hydrogen atoms on the MoO3–ZrO2 surface. Then the hydrogen atom becomes a proton by donating an electron to an adjacent Lewis acid site. The rate-controlling step involves the surface diffusion of hydrogen atoms and has an activation energy of 62.8 kJ/mol. A comparison of the hydrogen adsorption on SO42−–ZrO2, WO3–ZrO2 and MoO3–ZrO2 catalysts is discussed

Investigation of palladium-mesostructured silica nanoparticles (Pd-MSN) as anode electrocatalyst for alkaline direct methanol fuel cell

The commercialization of fuel cells is hindered by the high cost of noble metal electrocatalysts, such as platinum. Mesostructured silica nanoparticles (MSNs), as a novel catalyst support, are added to active palladium nanoparticles to create a Pd-MSN electrocatalyst with low Pd content to improve catalytic efficacy and decrease costs. Wet impregnation method was used to prepare catalysts that comprise palladium nanoparticles supported on MSNs (i.e. 5 wt% Pd-MSN, 10 wt% Pd-MSN, 15 wt% Pd-MSN, 20 wt% Pd-MSN and 20 wt% Pd-C) to enhance electrocatalytic activity for methanol oxidation. The structures of the catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) and Brunauer–Emmet–Teller (BET) surface area analysis, and their electrocatalytic performance towards methanol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Amongst the catalysts, 20 wt% Pd-MSN has the highest electrocatalytic activity (14.3 mA cm−2) and stability (3600 s) for methanol oxidation in alkaline medium at the constant potential of −0.2 V. This result indicates that 20 wt% Pd-MSN may be a promising anode material for direct methanol fuel cells. The improved electrocatalytic activity and stability of the electrocatalyst are attributed to the high specific surface area of MSN and the effective surface structure of Pd nanoparticles. Furthermore, MSN increases catalyst dispersion by producing new active sites, which results in the promotion of Pd utilization

Recent Application of Core-Shell Nanostructured Catalysts for CO₂ Thermocatalytic Conversion Processes

Carbon-intensive industries must deem carbon capture, utilization, and storage initiatives to mitigate rising CO2 concentration by 2050. A 45% national reduction in CO2 emissions has been projected by government to realize net zero carbon in 2030. CO2 utilization is the prominent solution to curb not only CO2 but other greenhouse gases, such as methane, on a large scale. For decades, thermocatalytic CO2 conversions into clean fuels and specialty chemicals through catalytic CO2 hydrogenation and CO2 reforming using green hydrogen and pure methane sources have been under scrutiny. However, these processes are still immature for industrial applications because of their thermodynamic and kinetic limitations caused by rapid catalyst deactivation due to fouling, sintering, and poisoning under harsh conditions. Therefore, a key research focus on thermocatalytic CO2 conversion is to develop high-performance and selective catalysts even at low temperatures while suppressing side reactions. Conventional catalysts suffer from a lack of precise structural control, which is detrimental toward selectivity, activity, and stability. Core-shell is a recently emerged nanomaterial that offers confinement effect to preserve multiple functionalities from sintering in CO2 conversions. Substantial progress has been achieved to implement core-shell in direct or indirect thermocatalytic CO2 reactions, such as methanation, methanol synthesis, Fischer–Tropsch synthesis, and dry reforming methane. However, cost-effective and simple synthesis methods and feasible mechanisms on core-shell catalysts remain to be developed. This review provides insights into recent works on core-shell catalysts for thermocatalytic CO2 conversion into syngas and fuel