A feasibility analysis of hydrogen delivery system using liquid organic hydrides

The paper discusses the techno-economic feasibility of a hydrogen storage and delivery system using liquid organic hydrides (LOH). Wherein, LOH (particularly cycloalkanes) are used for transporting the hydrogen in chemical bonded form at ambient temperature and pressure. The hydrogen is delivered through a catalytic dehydrogenation process. The aromatics formed in the process are used for carrying more hydrogen by a subsequent hydrogenation reaction. Cost economics were performed on a system which produces 10 kg/h of hydrogen using methylcyclohexane as a carrier. With proprietary catalysts we have demonstrated the possibility of hydrogen storage of 6.8 wt% and 60 kg/m³ of hydrogen on volume basis. The energy balance calculation reveals the ratio of energy transported to energy consumed is about 3.9. Moreover, total carbon footprint calculation for the process of hydrogen delivery including transportation of LOH is also reported. The process can facilitate a saving of 345 tons/year of carbon dioxide emissions per delivery station by replacing gasoline with hydrogen for passenger cars. There is an immense techno-economic potential for the process.     

Efficient hydrogen supply through catalytic dehydrogenation of methylcyclohexane over Pt/metal oxide catalysts

This paper describes the results of experiments on dehydrogenation of methylcyclohexane over Pt supported on metal oxides (Pt/MO) and Pt supported on perovskite (Pt/Per) catalysts. The reaction is being considered as a means for delivery of hydrogen to fueling stations in the form of more easily transportable methylcyclohexane. Among Pt/MO catalysts, the best activity as determined by the hydrogen evolution rate was observed over Pt/La₂O₃ catalyst at 21.1 mmol/g_met/min. Perovskite-supported catalysts exhibited relatively higher activity and selectivity, with Pt/La_0.7Y_0.3NiO₃ giving the best performance. This Pt/Per catalyst had an activity of ca 45 mmol/g_met/min with nearly 100% selectivity towards dehydrogenation. The catalysts were characterized using XRD, CO-chemisorption and SEM-EDXA techniques. The present study reports catalysts that minimize the use of Pt and explores tailoring the properties of the perovskite structure.     

Desorption of hydrogen from Ti–Zr–Ni hydrides using a mass spectrometer

We have performed thermogravimetry (TG) and mass-spectrometry measurements of hydrogen desorbed from fully and partially hydrided ternary Ti–Zr–Ni amorphous, quasicrystalline and crystalline alloys, with four different initial compositions, where the Ti/Zr ratio ranged from 1 to 2.4. The icosahedral, quasicrystalline Ti–Zr–Ni samples were obtained using the melt-spinning technique, and with subsequent annealing of these ribbons at 700 °C for 2 h in vacuum we were able to obtain a mixture of crystalline C14 Laves and α/β solid-solution phases. In addition, using subsequent mechanical alloying we produced amorphous powders of Ti–Zr–Ni from the as-spun ribbons. These various samples were then hydrided and analyzed by TG and mass spectrometry. The TG measurements provided us with the mass% of desorbed hydrogen, whereas the mass-spectrometry revealed information about the hydrogen desorption temperatures in the material. Despite the fact that the amorphous and icosahedral samples undergo some crystallization during the desorption measurements, the resulting mass spectra were different and were closely related to the alloy's structure. In contrast, the shapes of mass spectra were less affected by the composition, the total amount of desorbed hydrogen and the loading pressure.     

NbF5 additive improves hydrogen release from magnesium borohydride

The dehydrogenation properties of Mg(BH₄)₂ with various additives (SiO₂, VCl₃, CoCl₂ and NbF₅) were investigated. The addition of NbF₅ significantly improved the extent of hydrogen release as well as the kinetics. While neat Mg(BH₄)₂ starts to release hydrogen >270 °C, Mg(BH₄)₂ with NbF₅ begins hydrogen release ∼75 °C, as confirmed by mass spectrometry and thermogravimetry. The maximum hydrogen yield of Mg(BH₄)₂, obtained in the presence of 15 wt% NbF₅, was 3.7, 7.4, 10.0, 11.4 wt% for 150, 250, 300 and 350 °C, respectively. Using pXRD, we confirmed that the final crystalline product at 300 °C from Mg(BH₄)₂ + 15 wt% NbF₅ was Mg, while it was MgH₂ for neat Mg(BH₄)₂. Solid state ¹¹B NMR analysis of Mg(BH₄)₂ with 15 wt% NbF₅ at 300 °C showed significant selectivity toward the formation of Mg(B₁₂H₁₂) as intermediate, while neat Mg(BH₄)₂ showed β-Mg(BH₄)₂, Mg(B₂H₆) as well as some Mg(B₁₂H₁₂). Our results demonstrate that NbF₅ is a promising additive to provide high hydrogen yield values from Mg(BH₄)₂ at moderate temperatures <300 °C.     

Simple chemical processes based on low molecular-mass alkanes as chemical feedstocks

The present state of new developments in direct catalytic conversion of low-molecular-mass alkanes (C₁–C₃) to petrochemical feedstocks and petrochemicals is reviewed. Special attention is given to the following reactions: methane to methanol and formaldehyde by partial oxidation as well as to C₂ hydrocarbons by oxidative coupling, ethane and propane to their olefins by oxidative dehydrogenation and to their oxygenates, i.e., acetic acid, acrylic acid and acrolein by partial oxidation. Specific research results are presented on the oxidative dehydrogenation of ethane and propane.     

Mo_2C/CCA催化剂制备及环己烷脱氢性能研究

以(NH4)6Mo7O24.4H2O为钼源,以覆炭γ-Al2O3(CCA)为载体,采用浸渍法制备出催化剂前驱物Mo3O/CCA。以正己烷为渗碳剂对前驱物进行碳化得到Mo2C/CCA。对不同碳化终温下制得的催化剂进行了XRD表征。在固定床反应装置上进行了环己烷脱氢反应,考察了催化剂的制备条件及反应条件对催化剂脱氢活性的影响。结果表明:当载体CCA覆炭量为7.82%,碳化终温为650℃,反应条件为温度475℃、压力0.1 MPa、空速2h-1、氢烃体积比200∶1时,环己烷的转化率最高可达91%。     

含吡啶环的十聚钨酸季铵盐催化合成环己酮

以十聚钨酸季铵盐（[Bun Py]4W10O32）为催化剂、质量分数30%的H2O2为氧化剂,研究了环己醇催化氧化生成环己酮的反应,考察了反应时间、反应温度、H2O2和催化剂的物质的量等因素对此反应的影响。得出了此反应的最佳条件：反应温度为80℃,催化剂物质的量为0.06mmol,H2O2物质的量为125mmol,环己醇物质的量为50mmol,回流反应8h。在最佳反应条件下,环己醇的转化率为86.5%,环己酮的选择性可达到98.3%。反应后催化剂不溶于反应体系,简单过滤即可回收,重复使用3次后其活性基本不变。     

Characterization and reactivity of VMgO catalysts prepared by wet impregnation and sol–gel methods

This paper reports the study of physicochemical, surface, and catalytic properties of two series of VMgO catalysts prepared by two different methods: wet impregnation and sol–gel. The characterizations of the elaborated materials were performed using N₂-sorption (Brunauer, Emmett and Teller (BET)), X-ray diffraction, Raman, transmission electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analyses. The catalytic properties of the elaborated materials were investigated in the isopropanol decomposition reaction to determine their acid–base character and in the selective oxidation of n-butane to evaluate their dehydrogenation properties. The preparation method and vanadium content strongly affected the properties of our materials. The sol–gel method leads to smaller crystallite size, higher specific surface area, and uniform particle distribution compared to the impregnation one. Both impregnation and SG solids promote the formation of acetone, which is related to the presence of strong basic sites (O^2? species) on the catalytic exposed surface. The more pronounced basic character was obtained through the SG samples. The sol–gel samples exhibited the highest catalytic activity and C4-olefin selectivity in the partial oxidation of n-butane. Whatever the preparation procedure, the nature of surface oxygen species plays an important role in the orientation of catalytic performances.     

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

Molecular hydrogen is the simplest and most abundant compound in the universe and is involved in numerous industrial chemical processes. In conventional chemistry, dihydrogen typically plays the role of a reductant and a reagent for homogeneous and heterogeneous hydrogenation processes such as the industrial and enzymatic ammonia formation, reduction of metallic ores and hydrogenation of unsaturated fats and oils. However, there are also processes in which molecular hydrogen participates as promoter, and even as catalyst. The catalytic role of the dihydrogen in free-valence migration in irradiated polymers and the interstellar isomerization of the formyl cation (protonated carbon monoxide) are well-documented examples of such processes. Recently, this issue has received new attention. Dihydrogen has been shown to play the role of a dehydrogenation catalyst (involving particularly metallocomplexes and inorganic materials), a relay (pass-on) transfer molecular agent and a transporter of protons.

This review article, combined with original results, is focused on the mechanisms of the chemical processes where dihydrogen demonstrates catalytic behavior. We will call these processes (with somewhat broader meaning of the term) “dihydrogen catalysis” (DHC) which also includes the reactions mediated by transition metal dihydrides. Dihydrides are tentatively considered as pre-activated dihydrogen, coordinated to a metal center or implanted into a solid surface/support.

DHC reactions are classified into five major reaction types: (i) dihydrogen-assisted relay transport of H-atoms (H2-RT); (ii) dihydrogen-assisted stepwise relay transport of H-atoms or of a free valence (sH2-RT); (iii) dihydrogen-assisted proton transport (H2-PT); (iv) dihydrogen-assisted dehydrogenation (H2-DeH); and (v) pre-activated dehydrogenation (PA-DeH). The classification of these mechanisms is based on a detailed analysis of numerous potential energy surfaces studied by DFT and ab initio methods in conjunction with available experimental data. The H2-RT, H2-DeH, and PA-DeH processes occur via cyclic transition states. The relay H2-RT transport involves the H-H-H triad linked to both H-donor and H-acceptor centers, whereas the transition state ring in the H2-DeH dehydrogenation processes involves a H-H-H-H tetrad with the dihydrogen catalyst located in the middle. The H2-PT mechanism provides the transport of a proton mediated by dihydrogen combined in a triangular (H₃⁺)-carrier unit.

There are also practically important processes stimulated by dihydrogen such as the hydrogen spillover and hydrogen build-up in electronics, in which the catalytic role of dihydrogen is ambiguous, either because of the uncertainties in mechanisms, or prevailing traditional views. Some examples are briefly discussed in the framework of the concept of dihydrogen catalysis, some being provided with theoretical support (in part calculated by us), and others being merely hypothesized to provide suggestions to an interested reader.     

丙烷脱氢氧化制丙烯热力学分析

计算了丙烷脱氢过程各主、副反应的热力学平衡常数和平衡转化率,分析了平衡转化率、烧氢率与反应热效应的关系。表明氧化烧氢具有提高平衡转化率和能量合理利用的优点;丙烷脱氢平衡转化率随烧氢率的增加而增大;当反应温度为923K时要保证热量耦合,烧氢率应大于48.6%;丙烷脱氢氧化工艺原理在于用氧化再热取代传统中的过热蒸汽再热。