Browsing by Author "Shen, Ziqi"

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    An investigation of a novel monolithic nickel-based catalyst for clean hydrogen production
    (Cranfield University, 2024-05) Shen, Ziqi; Clough, Peter T.; Nabavi, Seyed Ali; Wagland, Stuart T.
    The decarbonisation of the energy sector can anticipate the future of net zero, and hydrogen is currently one of the most promising energy carriers to contribute to this goal. As for hydrogen production, steam methane reforming (SMR) occupies the predominant status and will remain in its position in the short term. The SMR process requires high-performance catalysts such as nickel-based catalysts, and carbon capture technology is of interest to decarbonise the SMR to produce clean hydrogen. The overall aim of the PhD project is to develop a novel monolithic nickel-based catalyst and evaluate its performance under SMR and sorbent-enhanced SMR (SE-SMR) conditions. The literature review looked back on the ceramic materials used in the SMR and SE-SMR processes, and also the method to prepare nickel-based catalysts. Silicon carbide was chosen as the support material due to its excellent thermal and mechanical properties. The monolithic nickel-based catalysts were designed, synthesised, characterised and tested in a fixed-bed reactor, in which the main reactor pipe and the steam generator were designed and constructed for this project. In addition, a pulse injection system was designed and installed on the reactor, and the SMR kinetics were studied using the monolithic catalysts. After the integration of the solid sorbents, a further study was conducted on the effect of structure within the SE-SMR process using the monolithic catalysts. The monolithic catalysts exhibited excellent activity at low SMR temperatures and pressures with a realistic gas space velocity. A kinetic model was established to describe the reaction rates using a novel and time-saving approach. The mass transfer limitations led to a low activation energy in kinetics and a reduction in activity when sorbents were applied. The monolithic catalysts will be a strong candidate for the decarbonisation of the energy sectors, with further improvement of its long-term stability and coordination with appropriate sorbents.
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    Data: Using a monolithic nickel-based catalyst under steam methane reforming
    (Cranfield University, 2023-12-12 15:04) Shen, Ziqi
    This dataset is the experimental data collected from a fixed bed reactor using monolithic catalysts. The reaction related is steam methane reforming (SMR) and tests were performed under different operating temperture, different nickel loading and different gas hourly space velosity (GHSV).
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    Design and performance testing of a monolithic nickel-based SiC catalyst for steam methane reforming
    (Elsevier, 2024-01-25) Shen, Ziqi; Nabavi, Seyed Ali; Clough, Peter T.
    Hydrogen is a highly promoted carbon-free energy carrier that has drawn significant attention recently due to its potential to decarbonise energy sector. More than three-quarters of hydrogen is currently produced via steam methane reforming (SMR), and nickel-based catalysts are used in most applications. Structured catalysts have been reported to be able to further improve catalyst performance as they can optimise heat and mass transfer, as well as prevent coke formation with its structural and textural proprieties. Silicon carbide (SiC) has excellent hardness, thermal conductivity, and chemical inertness, therefore is a promising material to develop structured nickel-based monolithic SiC catalysts for SMR. In this work, a structured monolithic catalyst support has been formed by a modified freeze-gelation method, initially starting from SiC powder, and nickel has been distributed to form a monolithic nickel-based catalyst by wet impregnation. The results showed that the catalysts can achieve thermodynamic equilibrium at 600 °C with a gas hourly space velocity (GHSV) of 10,000 h−1, while reaching a high methane conversion of 86% at 800 °C and GHSV value of 20,000 h−1 during the performance tests using low feeding concentration and low pressure. This is the first time SiC catalytic materials have had their performance demonstrated for SMR under realistic operating conditions.
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    Experimental and DFT study of (sorption-enhanced) steam methane reforming over bimetallic Ni-Cu catalysts
    (Elsevier, 2025-02-01) Wang, Siqi; Shen, Ziqi; Osatiashtiani, Amin; Nabavi, Seyed Ali; Clough, Peter T.
    The catalytic performance of a monometallic Ni/Al2O3 and three bimetallic Ni-Cu catalysts (with Cu loading of 2.5, 5, and 7.5 mol%, respectively) for the (sorption-enhanced) steam methane reforming reaction was evaluated. Physico-chemical characterization of the materials confirmed the formation of Ni-Cu alloy and the even distribution of active metals within the porous high-surface area support. All three bimetallic catalysts showed enhanced methane conversion compared to the conventional Ni/Al2O3 catalyst at higher temperatures (800 °C), which was attributed to the promotion of the water–gas shift reaction by the addition of Cu. The experimental observations were supported by the Density Functional Theory calculations of carbon and oxygen adsorption on the mono and bimetallic surfaces. Ni3Cu1 and Ni1Cu1 were calculated to have a similar level of catalytic activity as Ni, based on results from a microkinetic model of the steam methane reforming reaction. Ni1Cu3 showed slightly lower activity, potentially due to its low carbon adsorption ability which impedes the rate-determining methane decomposition process. The SMR reaction was further improved by adding calcium oxide as the CO2 sorbent, which increased both methane conversion and hydrogen yield. Ni3Cu1/Al2O3 and Ni1Cu1/Al2O3 were identified as promising SMR catalysts with a high methane conversion of approximately 90 % at 800 °C and 97 % at 700 °C, without and with the sorbent, respectively.
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    Intrinsic kinetics of steam methane reforming over a monolithic nickel catalyst in a fixed bed reactor system
    (Elsevier, 2024-11-05) Shen, Ziqi; Nabavi, Seyed Ali; Clough, Peter T.
    The intrinsic kinetics of steam methane reforming were experimentally investigated using a monolithic nickel-based catalyst in a specially designed fixed bed system. All kinetic tests were performed under various operating conditions: steam to carbon ratio of 2 to 5, methane volumetric concentration in feed gas of 3 % to 9 %, temperature of 500 to 650 °C, and typical biogas compositions with N2 dilution (carbon dioxide 35.7–55.6 %, methane 44.4–64.3 %, with 86–91 % nitrogen dilution). A deconvolution process was applied during the rate calculation and the reaction orders with respect to different gases were determined, coupled with thermodynamic system analysis. The reaction mechanism was then proposed and a Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model was established, followed by kinetic parameter estimations for the model and a further model validation with experimental data. Based on the model, the intrinsic kinetic of SMR reaction using monolithic catalysts was described. The validity and feasibility of applying the faster approach for kinetic parameter estimation were demonstrated, and this work is the first demonstration of a complex reaction system. Also, the reaction mechanism appeared to show a suitably high correlation with alternative and more sustainable methane sources (i.e. biogas).
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    An investigation of monolithic nickel-based catalyst for clean hydrogen production with CCS technology: the effect of structure
    (Elsevier, 2024-09-01) Shen, Ziqi; Nabavi, Seyed A.; Clough, Peter T.
    At present, hydrogen is recognised as a carbon-free energy carrier, but its major production via the steam methane reforming (SMR) process requires further decarbonisation as a considerable amount of carbon dioxide is simultaneously emitted. Carbon capture and storage (CCS) techniques can be integrated with typical SMR to produce clean hydrogen. Previously, a novel structured catalyst (Ni/SiC-M) was developed, and it was highly active for SMR under low operating temperature and high gas space velocity. By integrating CCS techniques, this structured catalyst is promising to produce clean hydrogen, however, there is a lack of knowledge about the catalytic performance when CCS is applied, especially the effect of structure. In this work, the feasibility of producing cleaner hydrogen with monolithic catalysts (Ni/SiC-M) coupled with sorbent particles was discussed. Different modified structures were applied for performance evaluation with a fixed bed reactor, to better understand the relationship between the structure and the activity. The results showed that sorbent particles can adsorb most of the generated carbon dioxide, leading to a higher hydrogen purity; the limitation of internal mass transfer caused by high pressure drops can result in a decrease in catalytic activity, but the impact was limited. The pore size could be the key factor to influence the performance of structured catalysts.
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    Ni-based bimetallic catalysts for hydrogen production via (sorption-enhanced) steam methane reforming
    (Elsevier, 2024-04-15) Wang, Siqi; Shen, Ziqi; Osatiashtiani, Amin; Nabavi, Seyed Ali; Clough, Peter T.
    The catalytic performance of a monometallic Ni/Al2O3 and three bimetallic catalysts (Ni3M1/Al2O3, with M = Cu, Fe, and Ge) for the (sorption-enhanced) steam methane reforming reaction was evaluated. Ni3Cu1/Al2O3 was found to be the optimal catalyst in terms of methane conversion, hydrogen yield, and purity. Ge also has a promoting effect on the monometallic Ni catalyst, whereas the addition of Fe negatively influenced its performance. Physico-chemical characterization of the materials indicated the formation of alloys upon activation of the materials with hydrogen. The addition of Cu increased the surface area and metal dispersion, and improved the overall morphology of the catalyst. The experimental observations were also supported by a numerical study combining Density Functional Theory-based calculations and Microkinetic modelling of the SMR process. Ni3Cu1 and Ni3Ge1 were calculated to have a similar level of catalytic activity as Ni, whereas Ni3Fe1 was unsuitable for the reaction. The SMR reaction was further improved by adding calcium oxide as the CO2 sorbent, which increased methane conversion, CO selectivity, hydrogen yield, and hydrogen purity. The highest methane conversion of 97 % was achieved by Ni/Al2O3 and Ni3Cu1/Al2O3 at 700 °C.