Hongchen Guo

A review on research progress in the direct synthesis of hydrogen peroxide from hydrogen and oxygen: noble-metal catalytic method, fuel-cell method and plasma method

Hydrogen peroxide (H2O2) as a highly efficient and green oxidant has become one of the 100 most important chemicals in the world. Some current research progress in the direct synthesis of H2O2 from H2 and O2 by noble-metal catalyst, fuel cell and plasma methods has been reviewed systematically in this paper. Perspectives about the development direction and application prospect of the above-mentioned three methods have also been discussed.

Safe Direct Synthesis of High Purity H2O2 through a H2/O2 Plasma Reaction

Extensive studies have been done on direct H2O2 synthesis from a H2/O2 mixture. To achieve high efficiency, direct H2O2 synthesis is generally performed in acidified solvent over supported noble-metal catalysts (Au, Pd, Au–Pd, and Pd– Pt). However, the direct synthesis of H2O2 from a H2/O2 mixture catalyzed by metals is quite hazardous, and it is very difficult to directly obtain high-purity and high-concentration H2O2. Research 13] published in the 1960s has demonstrated that H2O2 can be generated in H2/O2 non-equilibrium plasma through free-radical reactions in the absence of any catalyst or chemical. However, this plasma method has not yet drawn much attention, owing to low H2O2 yield (less than ca. 5%) and safety concerns about the discharge-triggered H2/O2 reaction. The content of O2 must be strictly controlled below 4 mol % in order to prevent explosion and ignition. Our previous research showed that the structure of the plasma reactor played an important role in the direct synthesis of H2O2. A H2/O2 mixture containing 3 mol% of O2 reaches 100% O2 conversion, but the H2O2 selectivity is only 3.5% (based on O2) in a single dielectric barrier discharge (SDBD) plasma reactor with a naked metal highvoltage (HV) electrode and an aqueous grounding electrode. On the other hand, 57.8% O2 conversion and 56.3 % H2O2 selectivity (based on O2) can be obtained by using a double dielectric barrier discharge (DDBD) plasma reactor with a pyrex-covered metal HV electrode (the pyrex cover acts as an additional dielectric barrier) and an aqueous grounding electrode. Although the selectivity has been greatly improved, the safety concerns and low efficiency, owing to low O2 content, are still big challenges. Herein, we report an experimental realization of controllable H2/O2 combustion processes by an optimized plasma reactor. High purity (Grade 1 electronic grade H2O2 according to the SEMI standard) and highly concentrated H2O2 solution (ca. 60 wt %) can be directly produced from a H2/O2 mixture without explosion. These results suggest a different mechanism from conventional H2/O2 combustion processes in the H2/O2 plasma reaction. As shown in Scheme 1, the electron activation of H2 into H is responsible for H2O2

Mechanism of seeding in hydrothermal synthesis of zeolite Beta with organic structure-directing agent-free gel

The organic structure-directing agent-free synthesis of zeolite Beta was carried out using several zeolite Beta seeds that differed in SiO2/Al2O3 ratio and crystal size. The synthesis was studied using X-ray diffraction, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy, ultraviolet-Raman spectroscopy, infrared spectroscopy, and N2 physisorption. Synthesis was successful using different zeolite Beta seeds including pure silica seeds. During the induction period, the seeds underwent dissolution. The SiO2/Al2O3 ratio and crystal size, pretreatment (calcination), and seed addition time had a significant influence on seed dissolution behavior, crystallization process, and product. Morphological studies revealed that the seed residues produced by dissolution (except for pure silica) resulted in the formation of “immobilized” surface nuclei, which allowed for the dense growth of fresh small zeolite Beta crystals. The dissolved small seed fragments yielded dispersed nuclei, which formed relatively scattered small zeolite Beta crystals thought to be the main nuclei source of the pure silica seed. It is suggested that the use of an appropriately high SiO2/Al2O3 ratio, small size, and precalcined zeolite Beta seed is helpful for the synthesis of highly crystalline and pure zeolite Beta from the organic structure-directing agent-free gel.

In Situ FT-IR Studies on Catalytic Nature of Iron Nitride: Identification of the N Active Site

Iron nitride has been widely used and played an important role in many catalytic processes, such as Haber–Bosch process (key intermediates), biological ammonia synthesis (nitrogen fixation), ammonia and hydrazine decomposition, NO removal, hydrodenitrogenation (HDN), and hydrodesulfurization (HDS), etc. The modification of properties of the Fe hosts upon N atom insertion into the closely packed metal lattice has been intensively studied by various techniques (Mçssbauer spectroscopy, XPS, LEED, XRD, and TEM) in terms of the structure change, electronic and steric effects, magnetic properties, mechanical hardness, electrical conductivity, and corrosion resistance. In comparison with metallic Fe, the increasing density of state at the Fermi level for Fe in the form of iron nitride originates from the d-band contraction of the metal with elongated M M bonds caused by the introduction of N atoms. 22] This renders the excellent catalytic behavior of iron nitrides comparable to noble metals. However, the essence of the iron nitride in catalysis has remained ambiguous so far, and especially challenging is the precise understanding of the surface-active sites, such as the Fe site, the N site, or the joint Fe N sites on the surface of iron nitride. Thus, more insights are needed to clearly identify the active sites on iron nitride surface. Infrared spectroscopy (IR), with the ability to probe surface process at the molecular level, is a powerful technique to identify the surface active sites of heterogeneous catalysts. Q. Xin. et al. first reported IR spectroscopic investigation on the nature of the surface sites of fresh Mo2N/Al2O3 by using CO as the probe molecule. Herein we report, for the first time, the identification of the N site as a chemically active center coexisting with the Fe site on the surface of iron nitride by using in situ FTIR coupled with CO, NH3, and H2-probe molecules. Moreover, the direct synthesis of amines from ethylene and ammonia were first achieved over iron nitride. Analysis of the adsorption of CO

Gas Phase Epoxidation of Propylene with TS-1 and in Situ H2O2 Produced by a H2/O2 Plasma

Gas phase epoxidation of propylene was performed by directly contacting propylene and gaseous H2O2 on the surface of TS-1 catalyst in an integrated reactor. The gaseous H2O2 was produced in situ by a H2/O2 plasma. The H2O2 formation rate can be enhanced by increasing the power density of the H2/O2 plasma reactor. The yield and selectivity for propylene oxide (PO) can be increased by optimizing the reaction conditions and using suitable TS-1 catalysts. With a power injection of 3.5 W, flow rates of H2, O2, and propylene of 170, 8, and 18 ml/min, respectively, catalyst loading of 0.8 g, and epoxidation temperature of 110 °C, the yield and selectivity for PO and the utilization rate of H2O2 were 246.9 g/(kg·h), 95.4%, and 36.1%, respectively. During the gas phase reaction, no decline of TS-1 activity was observed.

Effect of alkali metal ion modification on the catalytic performance of nano-HZSM-5 zeolite in butene cracking

Nano-HZSM-5 was modified by different alkali metal ions; the effect of the modification on its acidity and catalytic performance in butene cracking was investigated by using NH3-TPD characterization and catalytic evaluation in a small fixed-bed reactor. The results indicated that although the catalysts modified with various ions of Li, Na and K are different in their metal loading required to achieve the highest selectivity to ethylene and propylene, the best selectivity value obtained over all these modified catalysts is located in 50–60%. The activity of the alkali modified catalysts decreases slowly with the extension of the reaction time on stream; however, the selectivity to ethylene and propylene does not increase accordingly. The conversions of different butene isomers over the zeolite catalysts are decreased in the sequence of butene-1 > trans-butene-2 > cis-butene-2 > iso-butene, which may reflect the order of their reactivity towards cracking.

Methane formation route in the conversion of methanol to hydrocarbons

Abstract The influence factors and paths of methane formation during methanol to hydrocarbons (MTH) reaction were studied experimentally and thermodynamically. The fixed-bed reaction results show that the formation of methane was favored by not only high temperature, but also high feed velocity, low pressure, as well as weak acid sites dominated on deactivated catalyst. The thermodynamic analysis results indicate that methane would be formed via the decomposition reactions of methanol and DME, and the hydrogenolysis reactions of methanol and DME. The decomposition reactions are thermal chemistry processes and easily occurred at high temperature. However, they are influenced by catalyst and reaction conditions through DME intermediate. By contrast, the hydrogenolysis reactions belong to catalytic processes. Parallel experiments suggest that, in real MTH reactions, the hydrogenolysis reactions should be mainly enabled by surface active H atom which might come from hydrogen transfer reactions such as aromatization. But H 2 will be involved if the catalyst has active components like NiO.

Direct and continuous synthesis of concentrated hydrogen peroxide by the gaseous reaction of H2/O2 non-equilibrium plasma

Under ambient conditions, H2O2 has been synthesized with 32.51% yield and 56.25% selectivity via the gas-phase reaction of H2/O2 non-equilibrium plasma.

Catalytic conversion of n-butane over Au-Zn-modified nano-sized HZSM-5

Abstract An Au-Zn-modified HZSM-5 catalyst was prepared using deposition-precipitation and wet impregnation methods. To obtain a better understanding of the relationship between catalyst characteristics and catalytic performance, a thorough study of various catalyst samples (HZSM-5, Au/HZSM-5, Zn/HZSM-5, and Au-Zn/HZSM-5) was performed. The interactions between Au and Zn species in Au-Zn/HZSM-5 were determined using ultraviolet-visible and X-ray photoelectron spectroscopies. Compared with Zn/HZSM-5, the introduction of Au to give Au-Zn/HZSM-5 effectively promotes the dehydrogenation and aromatization of n-butane, and also suppresses hydrogenolysis over Zn species. The n-butane conversion (70.8%) and selectivity for olefins and aromatics (61.98%) increased significantly. The dry gas selectivity also decreased significantly to 28.4%. Au-Zn-containing HZSM-5 is a useful catalyst for the conversion of light alkanes.

Direct Oxidation of Methane to Hydrogen Peroxide and Organic Oxygenates in a Double Dielectric Plasma Reactor

Hydrogen peroxide is an important green oxidizing agent. The conventional process for hydrogen peroxide production is the indirect anthraquinone process, which employs multiple unit operations, generates considerable waste, and requires significant energy input. Hence, the development of a simple and highly efficient process for the synthesis of hydrogen peroxide 3] is of great scientific and practical importance. The direct synthesis of H2O2 from H2 and O2 is a much greener route, and supported Pd and Au–Pd alloy catalysts are known to be effective. However, an inherent hazard of this direct route are the very wide flammability limits of H2/O2 mixtures (4– 94 mol %). Hence, safe working practices stipulate a H2 concentration below 4 mol %, and this limit greatly reduces the H2O2 formation rate. Natural gas, of which CH4 is the main component, is an inexpensive and abundant resource with a low environmental impact. Considerable efforts to develop processes for converting CH4 into more valuable products have been made. The most extensively studied processes are oxidative coupling of CH4 ; [11, 12] partial oxidation of CH4 to synthesis gas; [13] and the formation of oxygenated compounds, including methanol, formaldehyde, and formic acid. 20] To the best of our knowledge, H2O2 has not been effectively produced by oxidation of CH4, although H2 can be manufactured from CH4 and H2O2 can be produced by oxidation of H2. Spectroscopic evidence of the formation of H2O2 in a microwave discharge plasma of CH4/ O2 has been reported. [21] We have shown that the structure of the discharge reactor plays an important role in the direct synthesis of H2O2 with the plasma method. With a specially designed plasma reactor, an O2 conversion of 57.8 % with a H2O2 selectivity of 56.2 % can be obtained in the gaseous plasma of a H2/O2 mixture. Taking all these observations into account, the effective formation of H2O2 might be achieved by CH4/O2 discharge with a proper plasma reactor. Herein, we report that in a double dielectric (DD) plasma reactor a satisfactory yield of H2O2 can be achieved under ambient temperature and atmospheric pressure from a stoichiometric (1:1) feed of CH4 and O2 by using the plasma method. The oxidation of CH4 to H2O2 offers considerable advantages over the oxidation of H2 to H2O2 because valuable organic oxygenates (methanol, formaldehyde, and formic acid) can be effectively produced at the same time. Furthermore, a wide range of CH4 concentrations can be used without any explosion hazards. The DD plasma reactor was prepared according to our previous work; one modification is the use of a nonmetal composite high-voltage electrode. We call this reactor a DD plasma reactor because it uses two dielectrics. As shown in Table 1, when a CH4/O2 mixture containing 50 mol % O2 is fed into the DD plasma reactor at a total flow rate of 50 mL min 1 (CH4+O2), the reactor converts 90.8 % of the O2 and generates