微铬含量CO中温变换催化剂本征动力学的研究

微铬含量ＣＯ中温变换催化剂本征动力学的研究崔波，赵素芳，刘鹏照，宋世英，张洪全（青岛化工学院化学工程系，青岛２６６０４２）关键词：催化剂，一氧化碳变换反应，铁催化剂，动力学１前言一氧化碳变换反应是化学工业中制氢的重要反应，长期以来所用的一氧比碳中变催...     

Superconductivity induced by hydrogen anion substitution in 1111-type iron arsenides

Hydrogen is the simplest bipolar element and its valence state can be controlled from +1 to −1. We synthesized the 1111-type iron arsenides CaFeAsH and LnFeAsO_1−xH_x (Ln = lanthanide; 0 ⩽ x ⩽ 0.5) with the ZrCuSiAs type structure by a high-pressure synthesis method. The position and valence state of the substituted H were determined by neutron diffraction and density functional theory calculations. The close similarity in the structural and electrical properties of CaFeAsH and CaFeAsF indicated the formation of the hydride ion (H⁻), which is isovalent with the fluoride ion (F⁻), in the 1111-type iron arsenides. When some of the O²⁻ ions in LnFeAsO are replaced by H⁻, superconductivity is induced by electron doping to the FeAs-layer to maintain charge neutrality. Since the substitution limit of hydrogen in LnFeAsO (x ≈ 0.5) is much higher than that of fluorine (x ≈ 0.2), the hydrogen substitution technique provides an effective pathway for high-density electron-doping, making it possible to draw the complete electronic phase diagram of LnFeAsO. The x–T diagrams of LnFeAsO_1−xH_x (Ln = La, Ce, Sm, Gd) have a wide superconducting (SC) region spanning the range x = 0.04–0.4, which is far from the parent antiferromagnetic region near x = 0.0. For LaFeAsO_1−xH_x, another SC dome region was found in the range x = ∼0.2 to ∼0.5 with a maximum T_c = 36 K, in addition to a conventional SC dome located at x ∼ 0.08 with maximum T_c = 29 K. Density functional theory calculations performed for LaFeAsO_1−xH_x indicated that the newly observed T_c is correlated with the appearance of degeneration of the Fe 3d bands (d_xy, d_yz and d_zx), which is caused not only by regularization of the tetrahedral shape of FeAs₄ due to chemical pressure effects but also by selective band occupation with doped electrons. In this article, we review the recent progress of superconductivity in 1111-type iron (oxy)arsenides and related compounds induced by hydrogen anion substitution.     

Studies of carbonaceous species in alkali promoted iron catalysts during Fischer–Tropsch synthesis

The effects of La, Mg and Ca promoters on carbonaceous surface and bulk iron carbide species formed in the alkali promoted iron catalysts are studied under realistic Fischer–Tropsch synthesis (FTS) conditions. Compositions of bulk iron phase and phase transformations of carbonaceous species during pretreatment and FTS reaction were characterized using the temperature-programmed surface reaction with hydrogen (TPSR-H₂) and XRD techniques. Many carbonaceous species on surface and bulk were qualitatively and quantitatively identified by combined TPSR-H₂ and XRD spectra of the alkali promoted iron catalyst. These species, sorted by the their reactivity with H₂ from high to low, were recognized as (a) adsorbed, atomic carbon; (b) amorphous, lightly polymerized hydrocarbon or carbon surface species; (c) bulk carbides and (d) disordered and moderately ordered graphitic surface carbons. The results revealed that while the surface basicity of the iron catalyst increased the CO dissociation proceeds faster than carbon hydrogenation. This phenomenon leads to excessive carbon deposition and formation of inactive iron carbide phases and graphitic type carbonaceous surface species, and consequently leads to catalyst deactivation.     

A new application of the commercial high temperature water gas shift catalyst for reduction of CO2 emissions in the iron and steel industry: Lab-scale catalyst evaluation

In this study, we present a detailed investigation of a commercial iron-based high temperature water gas shift (HTWGS) catalyst (Johnson Matthey KATALCO^TM 71-6) in a new application: the production of hydrogen from blast furnace gas (BFG), which originates from iron and steel manufacturing. During the lab-scale catalytic testing under BFG conditions the catalyst demonstrated: 1) high water gas shift activity and stability; 2) minimal methanation at reduced steam to CO ratios; 3) high resistance towards H₂S impurities present in the feed. The results of post-characterization of the discharged samples confirm the robustness of KATALCO 71-6 towards BFG process conditions: no over-reduction of the catalytically active Fe₃O₄ phase and no formation of a less active FeS phase. An in situ X-ray absorption spectroscopy study revealed no over-reduction of the iron phase under BFG conditions and the stabilization of the iron phase by diffusion of chromium into the iron oxide matrix. The findings of this study demonstrate the suitability of the iron-based HTWGS catalyst KATALCO 71-6 for the production of hydrogen from BFG streams. Knowledge gained in this study is an essential step in the development and scale up of carbon capture and storage as well as carbon capture and utilization technologies, such as the sorption enhanced water gas shift (SEWGS) technology, aimed at reducing the CO₂ footprint during steel manufacturing.     

Synthesis of a new self-supported Mgy(CuxNi0.6-xMn0.4)1-yFe2O4 oxygen carrier for chemical looping steam methane reforming process

Novel self-supported Mg_y(Cu_xNi_0.6-xMn_0.4)_1-yFe₂O₄ with (y = 0, 0.05, 0.1, 0.15, and x = 0, 0.15, 0.3, 0.45, 0.6) oxygen carriers (OCs) are synthesized through the co-precipitation method. The synthesized OCs’ properties are characterized by X-ray powder diffraction (XRD), Raman spectra, transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and Thermogravimetric Analysis (TGA). The synthesized OCs are assessed in Chemical Looping Steam Methane Reforming (CL-SMR) process subject to different mesh sizes, reaction temperatures, Steam/Carbon (S/C) molar ratios, Mg concentrations, and Cu and Ni concentrations. The characterization of the OCs and process results indicate the contributive effect of Mg incorporation on the Cu_xNi_0.6-xMn_0.4Fe₂O₄ support structure. The redox results reveal that Mg_0.1(Cu_0.3Ni_0.3Mn_0.4)_0.9Fe₂O₄ OC is of the highest activity, even at low reduction temperatures. This OC exhibits the highest activity and stability with lowest coke deposition during 24 redox cycles at 650 °C and S/C = 2.5. The highest CH₄ conversion of about 99.4% and H₂ yield of about 84.4% are obtained.     

Metal-rich heterostructure of Ag-doped FeS/Fe2P for robust hydrogen evolution

The transition metal phosphides (TMPs) with highly active and low-cost are imperative electrocatalysts for hydrogen evolution reaction (HER). In particular, metal-rich interface engineering of iron phosphide could effectively modify the active sites for HER and accelerate the charge transfer, thus achieving the promoted efficiency. Herein, we report metal-rich heterostructure of Ag-doped Fe₂P shell attached to FeS core on Fe foams (FeS/Fe₂P–Ag@IF) for HER, which are synthesized by a simple hydrothermal method with subsequent low-temperature phosphorization. Notably, the phosphorization process simultaneously achieves the partial conversion of FeS to Fe₂P, and complete reduction of Ag₂S to Ag. Furthermore, the metal-rich structure of Fe₂P increases the active sites for hydrogen adsorption, which consequently contributes to hydrogen evolution. Simultaneously, the successful doping of metallic Ag enhanced the electroconductivity and the stability of the electrocatalyst. Benefiting from the ternary synergistic effect at FeS/Fe₂P–Ag@IF and metallic Ag doping, the optimal Ag-doped FeS/Fe₂P electrocatalyst exhibits a low overpotential of 214.9 mV at 100 mA cm^?2, even surviving at this large current density with long-term stability. This promising strategy involving metallic Ag doping may be a suitable option for the development of iron-based metal-rich phosphides heterostructured for HER.     

Gas Switching Reforming for syngas production with iron-based oxygen carrier-the performance under pressurized conditions

A four-stage Gas Switching Reforming for syngas production with integrated CO₂ capture using an iron-based oxygen carrier was investigated in this study. The oxygen carrier was first reduced using dry methane, where high methane conversion rate was achieved producing CO₂ and steam. Following the reduction stage is a transition to syngas production in an intermediate stage that begins with partial oxidation of methane while methane cracking dominates the rest of the stage. This results in substantial carbon deposition that gasifies in a subsequent reforming stage by cofeeding steam and methane, contributing to more syngas yield. Some of the deposited carbon that could not gasify during the reforming stage slip to the oxidation stage and get combusted by oxygen in the air feed to release CO₂, thereby reducing the CO₂ capture efficiency of the process. It is in this oxidation stage that heat is being generated for the whole cycle given the high exothermicity nature of this reaction. Methane conversion was found to drop substantially in the reforming stage as the pressure increases driven by the negative effect of pressure on both carbon gasification by steam and on the steam methane reforming. The intermediate stage (after reduction) was found less sensitive to the pressure in terms of methane conversion, but the mechanism of carbon deposition tends to change from methane cracking in the POX stage to Boudouard reaction in the reforming stage. However, methane cracking shows a tendency to reduce substantially at higher pressures. This is could be a promising result indicating that high-pressure operation would remove the need for the reforming stage with steam as no carbon would have been deposited in the POX stage.     

Thixotropic properties of multi-functional binder and compaction behaviour of the low alloyed binder-treated powder

A new multi-functional binder with adhesive and lubricant effect was designed, and the thixotropic properties of the binder components and the resulting binder, the adhesive effect and compaction behaviour of the binder-treated powder were investigated. The results demonstrate that the thixotropic components in the binder are polyethylene wax and microcrystalline wax. With the increase of polyethylene wax content, the critical solid–liquid shear stress of binders decreases gradually. The main lubrication components in the low-pressure and high-pressure stages during the compaction process are found to be polyethylene wax and microcrystalline wax, respectively. The fine metal or graphite additives are effectively bonded on the surface of iron particles and filled in the pits. The green density reaches 7.25?g?cm^?3 at 600?MPa when the content of polyethylene wax is 30%. From 400 to 750?MPa, the content of polyethylene wax corresponding to the minimum ejection pressure decreases from 20 to 0%.     

Modifying the structure of red mud by simple treatments for high and stable performance in COx-free hydrogen production from ammonia

Red mud (RM) modified by various treatments was used as a catalyst for ammonia decomposition. Catalytic activity measurements performed at 500 °C and differential conversions illustrated that the rate increases with a decrease in the size of Fe₃N_y nanoparticles formed during activation in NH₃ flow. Measurements at 700 °C showed that a catalyst prepared by digesting RM in 6 M HCl followed by calcination at 900 °C provides a stable ammonia conversion of 98.8 ± 0.5% for more than 70 h at a space velocity of 120 000 cm³ NH₃ h^?1 g_cat^?1. This rate is premier among all iron-based catalysts in terms of both activity and stability and even on par with the performance of other non-noble metal catalysts. Detailed characterization indicated Fe₃N_y species readily available on the surface as the active species. Results provided here enable the utilization of RM as an environmentally-friendly, highly efficient, and almost cost-free catalyst for CO_x-free hydrogen production.     

润滑剂添加量对铁基混合粉末工艺性能的影响

本文以硬脂酸锌和石墨作为润滑剂,研究了添加量对铁基混合粉末流动性和松装密度以及压制性能的影响。结果表明,当硬脂酸锌添加量为0.2%~0.6%时可以改善铁基混合粉末的流动性和松装密度,流动性能较原混合粉末提高2.2%~17.4%,松装密度能提高136.6%~149.3%,添加量超过0.6%时效果不明显。添加0.2%~1.0%的硬脂酸锌,粉末压缩性逐渐增加,添加量超过1.0%时,压缩性变差。同时添加硬脂酸锌与石墨时,随着石墨添加量的升高,混合粉末的松装密度和压制性能不断降低。