Promotional roles of second metals in catalyzing methane decomposition over the Ni-based catalysts for hydrogen production: A critical review

The thermocatalytic decomposition (TCD) of methane is considered as a milestone towards the production of valuable CO_x-free hydrogen and carbon nanomaterials without the use of steam or O₂. Previous reviews have been aimed at methane decomposition over the different catalysts, such as nickel-based catalysts, non-nickel-based catalysts, metal oxide-supported catalysts, and carbon-supported catalysts. The Ni-based catalysts are suitably applied for methane TCD process due to their high activity and low cost. However, the loss of activity and/or stability with reaction time is one of the most notable challenges in the use of Ni-based catalysts, and a number of studies on the roles of various factors in overcoming such a problem can be found in the literature. Recently, the use of the second metal as a promoter to control catalyst deactivation has attracted much attention. The present review focuses on classification of the different promoters based on the periodic table of elements, such as alkali metals, alkaline earth, transition metals, noble metals, and rare earth metals, and makes a detailed discussion on promotional roles in influencing their physicochemical properties and catalytic performance of the Ni-based catalysts. The generalized structure-performance relationship of the metals-doped catalysts may give an appreciated reference to the design of catalysts with highly pure hydrogen production and carbon nanomaterials. In addition, this review also covers the works on effects of the promoters on nature and morphology of the formed carbon nanomaterials. The use of transition metals (Fe, Co or Cu), noble metal (Pd or Pt), and rare earth metal (La) with a suitable loading as a promoter influenced performance and lifespan of the catalyst and the interaction of Ni particles with the support. Among these promoters, Cu, Pd, La, and Cu–Pd as a dopant have demonstrated superior performance, which was attributed to the capability of these elements in prohibiting carbon accumulation on the active Ni components.     

Hydrogen production through autothermal reforming of CH4: Efficiency and action mode of noble (M = Pt,Pd) and non-noble (M = Re,Mo, Sn) metal additives in the composition of Ni-M/Ce0.5Zr0.5O2/Al2O3 catalysts

Hydrogen production through autothermal reforming of methane (ATR of CH₄) over promoted Ni catalysts was studied. The control of the ability to self-activation and activity of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was achieved by tuning their reducibility through the application of different types (M = Pt, Pd, Re, Mo or Sn) and content (molar ratio M/Ni = 0.003, 0.01 or 0.03) of additive. The comparison of the efficiency and action mode of noble (M = Pt, Pd) and non-noble (M = Re, Mo, Sn) metal additives in the composition of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was performed using X-ray fluorescence analysis, N₂ adsorption, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction with hydrogen, and thermal analysis. The composition-characteristics-activity correlations were determined. It was shown that the introduction of a promoter does not affect the textural and structural properties of catalysts but influences their reducibility and performance in ATR of CH₄. At the similar dispersion of NiO active component (11 ± 2 nm), the Ni²⁺ reduction is intensified in the following order of additives: Mo < Sn < Re ≤ Pd < Pt. It was found that for the activation of Ni and Ni–Sn catalysts before ATR of CH₄ tests, the pre-reduction is required. On the contrary, the introduction of Pt, Pd and Re additives leads to the self-activation of catalysts under the reaction conditions and an increase of the H₂ yield due to the enhanced reducibility of Ni²⁺. The efficient and stable catalyst for hydrogen production has been developed: in ATR of CH₄ at 850 °C over an optimum 10Ni-0.9Re/Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst the H₂ yield of 70% is attained. The designed catalyst has enhanced stability against oxidation and sintering of Ni active component as well as high resistance to coking.     

碱减量促进剂在T/R混纺织物减量中的应用

论述了涤纶碱减量的基本原理，探讨了碱减量促进剂TF118L对减量率，碱利用率以及手感等的影响，得出了较佳的工艺条件。     

合成气直接制低碳烯烃铁基催化剂的研究进展

评述了近年来有关合成气直接制低碳烯烃铁基催化剂的研究进展,重点分析了铁基催化剂的活性相、载体、助剂对催化剂的活性、选择性等方面的影响,并对未来铁基催化剂的发展方向进行了展望。     

Selective hydrogenation of acetylene on Pd/SiO2 catalysts promoted with Ti, Nb and Ce oxides

Transition-metal oxides added to Pd/SiO₂ improve significantly the activity and the ethylene selectivity of the catalyst in acetylene hydrogenation, which is caused by the interaction between the oxides and the Pd surface similar to the case of the oxide-supported catalysts. It has been confirmed through experiments that metal oxides spread on and modify both geometrically and electronically the Pd surface after the catalyst is reduced at 500°C. Such a behavior of metal oxides in the catalyst is correlated well with their promotional effect on the catalyst performance. That is, the oxides on the Pd surface retard the sintering of the dispersed Pd particles, suppress the adsorption of ethylene in the multiply-bound mode, and facilitate the desorption of ethylene produced by acetylene hydrogenation. Among the three metal oxides examined in this study, Ti oxide is found to have the most promotional effect.     

Suitable combination of promoter and micellar catalyst for kilo fold rate acceleration on propanol to propionaldehyde conversion in aqueous media

Oxidation of propanol by chromic acid produces propionaldehyde under kinetic condition [propanol]_T ≫ [Cr(VI)]_T. This oxidation reaction is performed also in presence of micellar catalysts (anionic, cationic and neutral) and hetero-aromatic nitrogen bases promoters (picolinic acid, 2,2′-bipyridine, 1,10-phenanthroline) in aqueous media. The product is confirmed by 2,4-DNP test and ¹H NMR spectroscopy. Anionic surfactant sodium dodecyl sulphate (SDS), neutral surfactant triton X-100 (TX-100) accelerated the reaction both in presence and absence of promoters whereas cationic surfactant N-cetyl pyridinium chloride (CPC) inhibited the reaction. Combination of SDS and bipy is found to be the most efficient for this oxidation.     

The study of the uncalcined Au catalyst and inorganic salts on direct gas-phase epoxidation of propylene

This paper presents the results of the propylene epoxidation in co-presence of hydrogen and oxygen on both dried and calcined Au catalysts, which were prepared by liquid grafting method using Me₂Au(acac) as a precursor and trimethylsilylated Ti-MCM-48 as a support. The calcined catalyst shows PO activity at temperatures much higher and wider than the dried one. Addition of inorganic salts greatly modified the catalytic behaviors. CsNO₃ could be a promising promoter whereas KBr led to the production of propionaldehyde instead of propylene oxide.     

The analysis of core promoter sequences based on their chemical features

The biochemical behaviors of promoter sequences are closely associated with their chemical properties and structures. In this study, an approach to the analysis of promoter sequences was developed based on the chemical features in DNA sequences. Utilizing the chemical parameters of nucleotides, a string of character sequence was translated into numerical sequences, and then the profiles of chemical properties in the sequence can be observed, which are helpful to better understanding for the behaviors of the sequence. The proposed approach was applied to the analysis of core promoter sequences of Escherichia coli K-12. Apart from the validation of the motifs at the − 35 and − 10 regions, several possible functional sites were observed, and the interaction mechanism between promoter sequence and RNA Polymerase holoenzyme was explored. The obtained results indicate that the consensus of important chemical features is higher than that of the characters in sequences, and our study could provide biologists some valuable hints.     

Quantitative measurement of chromium's ability to promote adhesion

Using atomic force spectroscopy, we investigated the adhesion-promoting ability of chromium. An intermediate layer of chromium can overcome the low adhesion between metal films and silicon dioxide. For the first time, we quantitatively studied this experimentally well known fact. We compared the adhesion between chromium and different substrates such as gold, silver, mica, and silicon dioxide and, beyond that, the adhesion between silicon dioxide and the same substrates. To avoid additional effects due to water, we chose ethanol as a nonpolar solvent. Taking the interfacial energies of the surfaces with the liquid into account eliminates the direct influence of the fluid medium on the adhesion of the solid material. The results we obtained corroborate the experimental fact of higher adhesion of chromium with the chosen substrates, as well as substantiate the value of chromium as an adhesion promoter. The adhesion of chromium-coated probes on gold, silicon dioxide, and mica is higher than the adhesion of silicon dioxide probes on the same substrates.     

Hydrogen system using novel additives to catalyze hydrogen release from the hydrolysis of alane and activated aluminum

Herein, we present a new system for the generation of hydrogen for use in portable power systems utilizing a two-step process that involves the thermal decomposition of α-AlH₃ (10 wt% H₂) followed by the hydrolysis of the activated aluminum (Al*) byproduct to release additional H₂. This study focuses on the use of promoter additives (PA) to catalyze the hydrolysis of Al*. Our study has shown that the addition of water to a Al*:PA composite results in an instantaneous release of hydrogen at room temperature, without the use of transition metal catalysts. This secondary reaction increases the overall hydrogen content of the material even when the weight of the added water is accounted for. Additionally, a one-step process, in which water is added directly to the α-AlH₃:PA composite, was also examined. Large amounts of H₂ and heat are released immediately following the addition of water and could serve a means to shorten the start-up time of the fuel cell as well as assist in the thermal decomposition of α-AlH₃. Our study compares the use of different PA’s and presents novel composites made of α-AlH₃ and ionic hydride additives in an attempt to obtain the best performance of a hydrogen source based on α-AlH₃. The composites were characterized by TGA-RGA, XRD, and SEM before and after H₂ release.