Poly (acridine orange) film modified electrode for the determination 1-naphthol in the presence of 2-naphthol

The voltammetric behavior of 1-naphthol was studied with a poly (acridine orange) (PAO) film modified glass carbon electrode (GCE). The electrooxidation of 1-naphthol was an irreversible process with its oxidation overpotential at the PAO electrode 180 mV lower than that on the GCE. PAO electrode demonstrated electrocatalytic activity to the electrooxidation of 1-naphthol giving a greatly improved detection limit down to 8 × 10⁻⁸ mol L⁻¹(S/N = 3). At the optimal experimental condition, the oxidation peak current from the PAO electrode was linearly proportional to the concentration of 1-naphthol in the range of 2 × 10⁻⁷ to 3.2 × 10⁻⁶ mol L⁻¹ and 5.2 × 10⁻⁶ to 1.2 × 10⁻⁴ mol L⁻¹. The differences of the oxidation peak potentials between 1-naphthol and the coexisted 2-naphthol was 170 mV allowing the selective detection of 1-naphthol in a mixed solution with 2-naphthol. The detection of 1-naphthol in tap water and river water was carried out with satisfactory results.     

Preparation and electrochemical properties of functionalized ionic liquid self-assembled modified graphite electrode

A modified graphite electrode with functionalized ionic liquid (IL) pyridinium derivative of β-cyclodextrin ([CDbPy]BF₄) was prepared by layer-by-layer self-assembly technique. With ferrocene as probe, the characterization of the (CDIL/PDDA)_n/GE SAMs in the solution of phosphate (PBS, pH 7.0) was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry. The electrochemical behavior of p-chloronitrobenzene (p-CNB) at the modified electrode was studied. It was found that the modified electrode could catalyze the reduction of p-CNB and made the cathode peak move about 100 mV in positive direction in the solution of 0.1 mol/L PBS (pH 7.0). Differential pulse voltammetry (DPV) was applied to the determination of p-CNB in waste water with satisfactory results. The detection limit and the linear range of the concentration of p-CNB to the reduction peak current were 8.0 × 10⁻⁸ mol/L and 3.0 × 10⁻⁷–1.0 × 10⁻⁵ mol/L, respectively.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Amperometric glucose biosensor with high sensitivity based on self-assembled Prussian Blue modified electrode

A glucose biosensor, which was based on self-assembled Prussian Blue (PB) modified electrode with glucose oxidase (GOD) immobilized in cross-linked glutaraldehyde matrix, was developed. Fourier-transform infrared spectroscopy shows that the immobilized GOD retains its native conformation. Cyclic voltammetry was used to examine the electrocatalytic property of the enzyme electrode. The prepared glucose biosensor exhibits fast response (<4 s) and low detection limit of 5 × 10⁻⁶ M. The calculated apparent Michaelis constant K_M was 6.3 ± 1.2 mM, indicating a high affinity between the GOD and glucose. The effects of glutaraldehyde concentration and GOD loading on the sensitivity of the glucose biosensor have also been investigated. Under the optimal conditions, the biosensor shows a high sensitivity of about 80 mA M⁻¹ cm⁻² in a concentration range up to 1 × 10⁻³ M. The relative standard deviation (RSD) for intra-electrode and inter-electrode were 4% and 5%, respectively. In addition, the anti-interferent ability and stability of the biosensor were also discussed.     

Development and applications of quaternary ammonium (QA) membrane electrodes in pharmaceutical preparation and in bioavailability of Prostaglandin E1 and Deoxycholate

The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 × 10⁻⁷ M to 1.0 × 10⁻² M and 4.4 × 10⁻⁷ M to 1.0 × 10⁻² M with detection limit of 1.5 × 10⁻⁷ M and 3.3 × 10⁻⁷ M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5–7.5 and 4.0–7.0) with fast response times (11 s and 13 s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E₁ (PGE₁) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E₁ and Deoxycholate in plasma of different patients.     

Evaluation of atrazine degradation in UV/FeZSM-5/H2O2 system using factorial experimental design

Degradation of atrazine in model wastewater by UV/FeZSM-5/H₂O₂ system chosen as optimal for application of advanced oxidation process (AOP) has been studied in a batch photo reactor. The statistical study of the process was performed using two-level full factorial experimental design with the three process parameters. Individual parameters and their interaction effects on atrazine degradation were determined and statistical model of process was developed. The optimal operating conditions were established. This approach has also given a broader insight of the processes that were occurring in the reaction system, and it has finally led to simplification in terms of kinetics. Atrazine degradation was described by pseudo-first-order kinetics with observed rate constant k′ = 2 × 10⁻³ s⁻¹.     

PTFE-F-PbO2 电极在H2SO4溶液中的析氧行为

F-PbO2 electrode and polytetrafluoroethylene （PTFE） doped F-PbO2 electrode （PTFE-F-PbO2） were prepared on a plexiglas sheet substrate by a series of procedure including chemical and electrochemical depositions. The electrochemical activities of these two electrodes for oxygen evolution （OE） reaction were examined by electrochemical tests. In comparison with F-PbO2, PTFE-F-PbO2 electrode exhibited larger active surface area and higher oxygen vacancy deficiency, which resulted in its higher electrocatalytic activity for OE. In addition, both exchange current density and activation energy of the electrodes for OE were calculated in terms of active surface area. The values of exchange current density and activation energy in 0.5 mol·L^-1 H2SO4 aqueous solution were 1.125×10^ -3 mA·cm^-2 and 18.62 kJ·mol^-1 for PTFE-F-PbO2, and 8.384×10^-4 mA·cm^- 2 and 28.98 kJ·mol^-1 for F-PbO2, respectively. Because these values are calculated on the basis of the active surface areas of the electrodes, the enhanced activity of PTFE-F-PbO2 can be attributed to an increase in oxygen vacancy deficiency of PbO2 due to doping by PTFE. The influence of PTFE adulteration on the activity of PbO2 film electrode for OE was investigated in detail in this study.     

Kinetic studies on sorption of n-hexane in vanadium substituted MFI type zeolites of various crystal morphologies

The MFI type materials isomorphously substituted with vanadium form crystals of two morphology types. Investigations of sorption kinetics for n-hexane indicated for both morphologies a non-typical increase in the value of corrected transport diffusion coefficient with the crystals dimensions. An increase in the D₀ values with the vanadium content of the crystals has also been found, although it is not so well expressed as that with the dimensions. The increase in the D₀ values is from 1.1 × 10⁻¹¹ to 1.1 × 10⁻¹⁰ m²/s and may be a consequence of an additional system of larger pores, which is not reflected in the adsorption isotherms due to common occurrence of these pores in all crystals. It is also possible that vanadium causes a superior structure ordering and a decrease in/weakening of diffusion barriers.     

Highly sensitive, reusable electrochemical aptasensor for adenosine

A reusable electrochemical aptasensor for highly sensitive detection of small molecules had been developed using adenosine as a model molecule. The sensing interface was fabricated by self-assembling the part DNA duplex hybridized by 5′-thiolated part complementary strand (TPCS) and 3′-ferrocene(Fc)-labeled adenosine-binding aptamer strand (FABA) through S–Au bonding on a gold electrode surface. When the modified electrode was incubated in the adenosine solutions, the aptamer made structure switching to bind adenosine. As a result, Fc-labeled adenosine-binding aptamer strand was taken off from the sensing interface, resulting in a decrease of the redox current. The aptasensor was characterized electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV of the resulting aptasensor showed a linear response to the increase of the adenosine concentration in the range of 5.0 × 10⁻⁸–1.5 × 10⁻⁵ M with a linear correlation of r = 0.9898 and a detection limit of 1.65 × 10⁻⁸ M. Moreover, the aptasensor exhibited several excellent characteristics, such as high sensitivity, selectivity, good stability, and reproducibility.     

Voltammetric measurements of aminosalicylate drugs using bismuth film electrode

A bismuth film electrode (BiFE) prepared ex-situ on a supporting glassy carbon electrode exhibited convenient electroanalytical performance for voltammetric measurement of selected aminosalycilate drugs. The reduction behaviour of aminosalycilate drugs was studied in aqueous solutions within the pH range of 4–6. The voltammetric responses were compared with those obtained at the bare glassy carbon electrode under identical conditions. In the square-wave voltammetric operation mode the BiFE showed a linear response in the concentration range of 5 × 10⁻⁶ to 3.5 × 10⁻⁴ and 1 × 10⁻⁶ to 5 × 10⁻⁴ M for sulfasalazine and olsalazine, respectively. Its electrode surface revealed auspiciously high stability and remarkable reproducibility in the rapid analysis of aminosalycilate drugs. Finally, the BiFE was satisfactorily applied for direct quantitation of azo prodrugs in real pharmaceutical samples.     

Study of LiNi0.5Mn1.5O4 synthesized via a chloride-ammonia co-precipitation method: Electrochemical performance, diffusion coefficient and capacity loss mechanism

LiNi_0.5Mn_1.5O₄ powders are prepared via a new co-precipitation method. In this method, chloride salts are used as precursors and ammonia as a precipitator. The impurity of chlorine can be removed via a thermal decomposition of NH₄Cl in the subsequent calcination. X-ray diffraction pattern reveals that the final product is a pure spinel phase of LiNi_0.5Mn_1.5O₄. Scanning electron microscopy shows that the powders have an octahedron shape with a particle size of about 2 μm. Electrochemical test shows that the LiNi_0.5Mn_1.5O₄ powders exhibit an excellent cycling performance and after 300 cycles, the capacity retention is 83%. The lithium diffusion coefficient is measured to be 5.94 × 10⁻¹¹ cm² s⁻¹ at 4.1 V, 4.35 × 10⁻¹⁰ cm² s⁻¹ at 4.75 V and 7.0 × 10⁻¹⁰ cm² s⁻¹ at 4.86 V. The mechanism of capacity loss is also explored. After 300 cycles, the cell parameter ‘a’ decreases by 0.54% for the quenched sample (LiNi_0.5Mn_1.5O_4−δ) and by 0.42% for the annealed sample (LiNi_0.5Mn_1.5O₄). Besides, it is the first time to identify experimentally that the Ni and Mn ions dissolved in the electrolyte can be further deposited on the surface of anode.     

Tailor-made gold brush nanoelectrode ensembles modified with l-cysteine for the detection of daunorubicine

A new functionalized l-cysteine surface modified 3D gold brush nanoelectrode assembly BNEE (l-cys/BNEEs) was prepared. The BNEEs consisted of gold nanowires 100 nm in diameter and up to 400 nm in length fabricated by template synthesis in track etched polycarbonate membranes. The nanowires were exposed by controlled chemical etching of the membrane and were then modified by coating l-cys on the surface of the exposed gold nanowires. The morphology of the BNEEs was imaged by scanning electron microscopy and the real active area of BNEEs was determined by electrochemical impedance spectroscopy. The redox of daunorubicine (DNR) at the l-cys/BNEEs exhibited absorption-controlled characteristics and higher current activity than that at l-cys surface modified 2D disk NEEs (l-cys/DNEEs). The square wave voltammetry technique was employed to detect DNR. The detection limit was 1.0 × 10⁻⁸ M (s/n = 3). The linear detection concentration range of DNR was from 2.5 × 10⁻⁸ to 4.0 × 10⁻⁷ M.     

Electrical properties of V2O5–WO3/TiO2 EUROCAT catalysts evidence for redox process in selective catalytic reduction (SCR) deNOx reaction

Electrical conductivity measurements on EUROCAT V₂O₅–WO₃/TiO₂ catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH₃ to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH₃ without O₂, and (ii) 2000 ppm NO + 2000 ppm NH₃ + 500 ppm O₂) to put in evidence redox processes in SCR deNO_x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W⁶⁺ and V⁵⁺ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO₃/TiO₂ precursor of V₂O₅–WO₃/TiO₂ EUROCAT catalyst. It contained an average amount of 0.37 at.% W⁶⁺dissolved in titania, i.e. 1.07 × 10²⁰ W⁶⁺ cations dissolved/cm³ of titania. For the fresh catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved in titania were found to be equal to 1.07 × 10²⁰ and 4.47 × 10²⁰ cm⁻³, respectively. For the used catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved were found to be equal to 1.07 × 10²⁰ and 7.42 × 10²⁰ cm⁻³, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10²⁰ additional V⁵⁺ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO⁻ and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH₃ reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N^o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to

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. In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases.     

Urea release rate from a scoop of coated pure urea beads: Unified extreme analysis

Urea release from a scoop of coated beads in a given volume of a well stirred liquid has been investigated analytically and experimentally. A method for determining the fractional cumulative release and fractional release rate curves for the scoop without knowing particle number and radii is presented. The representative D/K_b for a scoop of urea beads spray coated with ethyl cellulose is near 3.5 × 10⁻⁸ cm²/s, and that with cellulose acetate phthalate is near 7 × 10⁻⁸ cm²/s.     

Impedance investigation of the mechanism of copper electrodeposition from acidic perchlorate electrolyte

The mechanism of the copper electrodeposition from acidic perchlorate electrolyte has been investigated with polarization and impedance methods. The impedance of the copper electrode in copper perchlorate electrolytes has been measured as a function of frequency for different Edc overpotential values and different copper(II) ion concentrations. The relations between the shape of a complex plane impedance display and the copper electrode potential values as well as the concentration of CuII ion were analysed in terms of the electrode reaction mechanism. It is shown, that the presence of the intermediate cuprous ion and its sinusoidal change of transport rate is one of the main factors determining the depressed shape of the impedance arc. The quantitative relation between the faradaic impedance and the rates of electrode reaction rates was established. The impedance arc was simulated with a set of parameters involving: rate constants, Tafel slopes, diffusion coefficient of cuprous ion and double layer capacitance. The rate constants were calculated with respect to ECu2 + Cu00 as: k10 = 6.50 × 10−5 cm s−1, k20 = 0.139 cm s−1, k−20 = 1.88 × 10−7 mol cm−2 s−1.     

Magnetic properties of CNX whiskers

Carbon–nitrogen whiskers have been prepared by pyrolysis of 1,2-diaminopropane at 950 °C or of allylamine at 900 °C followed by quenching. They are scrolls of carbon film typically 250 nm thick and up to 1 mm long with about five layers in a structure like a “cigare russe” or “brandy snap”, about 50 μm in diameter. Approximately 8 wt% of nitrogen is incorporated into the carbon films, which are practically amorphous, exhibiting a broad diffraction peak at d = 0.34 nm. The whiskers are on the border of metallic conductivity with a resistivity of about 10⁻⁶ Ωm, and they may show either a positive or a negative temperature coefficient of resistance. The pyrolysis produces either whiskers, soot or both. Magnetization measurements of the whiskers made from 1,2-diaminopropane reveal a large diamagnetic susceptibility of χ = −170 × 10⁻⁹ m³  kg⁻¹ and a small ferromagnetic component of unknown origin with σ_S of up to 0.2 A m² kg⁻¹, whereas the soot shows a purely diamagnetic signal, with χ ≈ −40 × 10⁻⁹ m³ kg⁻¹.     

Polyaniline–polyelectrolyte–gold(0) ternary nanocomposites: Synthesis and electrochemical properties

Ternary composites based on polyaniline (PAni), a polyelectrolyte-namely poly(diallyldimethylammoniumchloride) (PDDMAC) and gold (Au(0)) nanoparticles have been formulated and synthesized where the high concentration of PDDMAC acted as medium of reaction. The nanocomposites are characterized by FT-IR, UV–vis, XRD, XPS, SEM, AFM and TEM techniques. XRD showed the presence of all three viz., polyaniline, PDDMAC and Au(0) components in the ternary system. The composites exhibited higher conductivities in the range 26 × 10⁻⁶ to 217 × 10⁻⁶ S/cm compared with the binary composite of PAni–PDDMAC. The ternary composites were adsorbed on a GC electrode and used for sensing dopamine. The composites are useful in sensing as low as 0.05 mM concentration of dopamine at lower potential values compared to some binary PAni–Au nanocomposites.     

Carbon nanotube-supported Pd–ZnO catalyst for hydrogenation of CO2 to methanol

A type of Pd–ZnO catalysts supported on multi-walled carbon nanotubes (MWCNTs) were developed, with excellent performance for CO₂ hydrogenation to methanol. Under reaction conditions of 3.0 MPa and 523 K, the observed turnover-frequency of CO₂ hydrogenation reached 1.15 × 10⁻² s⁻¹ over the 16%Pd_0.1Zn₁/CNTs(h-type). This value was 1.17 and 1.18 times that (0.98 × 10⁻² and 0.97 × 10⁻² s⁻¹) of the 35%Pd_0.1Zn₁/AC and 20%Pd_0.1Zn₁/γ-Al₂O₃ catalysts with the respective optimal Pd_0.1Zn₁-loading. Using the MWCNTs in place of AC or γ-Al₂O₃ as the catalyst support displayed little change in the apparent activation energy for the CO₂ hydrogenation, but led to an increase of surface concentration of the Pd⁰-species in the form of PdZn alloys, a kind of catalytically active Pd⁰-species closely associated with the methanol generation. On the other hand, the MWCNT-supported Pd–ZnO catalyst could reversibly adsorb a greater amount of hydrogen at temperatures ranging from room temperature to 623 K. This unique feature would help to generate a micro-environment with higher concentration of active H-adspecies at the surface of the functioning catalyst, thus increasing the rate of surface hydrogenation reactions. In comparison with the “Parallel-type (p-type)” MWCNTs, the “Herringbone-type (h-type)” MWCNTs possess more active surface (with more dangling bonds), and thus, higher capacity for adsorbing H₂, which make their promoting action more remarkable.