Forced Unsteady State Operation of a Catalytic Converter during Cold Start-up for Oxidizing CO Over Pt/γ-Al2O3 Catalyst

CO oxidation in the catalytic converter hasn’t showed best performance particularly during cold start-up, since the catalyst is not active during this period. The purpose of this experiment was to develop the forced unsteady state operation procedure of CO oxidation using 0.05%-w Pt/γ-Al2O3 and space velocity of 0.406 mmol/s/gram. The catalytic converter was gradually ramped-up, while introducing the feed gas containing CO in the air. The feed gas was modulated following a square wave model with switching time variation at 3, 6, 15, and 30 s and various operation modes. To gain the intrinsic reaction rate, the external mass transfer criterion was determined. Ramping-up the temperature from 50 until 150°C increased the CO conversion with different profiles between steady state and dynamic flow rate. The dynamic system with modulated CO feed flow gave lower light-off temperature and higher average CO conversion than the steady state system which gave light off temperature 115°C and average CO conversion of 48.86%. The switching time of 3 s gave highest average CO conversion during ramping-up, which was 79.35%. Meanwhile the dynamic operation system with modulated feed flow gave higher lightoff temperature and lower average CO conversion than steady state system.

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Highly Reducible Nanostructured CeO2 for CO Oxidation

Catalysts ◽

10.3390/catal8110535 ◽

2018 ◽

Vol 8 (11) ◽

pp. 535 ◽

Cited By ~ 2

Author(s):

Gang Feng ◽

Weining Han ◽

Zhimiao Wang ◽

Fang Li ◽

Wei Xue

Keyword(s):

Electron Microscope ◽

Co Oxidation ◽

Hydrothermal Process ◽

Textural Properties ◽

Space Velocity ◽

X Ray Diffraction ◽

Transmission Electron ◽

Co Conversion ◽

Structure Morphology ◽

Adsorption Desorption

Ceria in nanoscale with different morphologies, rod, tube and cube, were prepared through a hydrothermal process. The structure, morphology and textural properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and isothermal N2 adsorption-desorption. Ceria with different morphologies were evaluated as catalysts for CO oxidation. CeO2 nanorods showed superior activity to the others. When space velocity was 12,000 mL·gcat−1·h−1, the reaction temperature for 90% CO conversion (T90) was 228 °C. The main reason for the high activity was the existence of large amounts of easily reducible oxygen species, with a reduction temperature of 217 °C on the surface of CeO2 nanorods. Another cause was their relatively large surface area.

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Comparison of Unsteady State and Quasi Steady State Modeling for Hydrocarbons in a Monolithic Catalytic Converter

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1688 ◽

2008 ◽

Vol 6 (1) ◽

Author(s):

Sanchita Chauhan ◽

V. K. Srivastava

Keyword(s):

Steady State ◽

Numerical Solutions ◽

Catalyst Surface ◽

Catalytic Converter ◽

Heterogeneous Reactions ◽

Exhaust Gas ◽

Quasi Steady State ◽

Unsteady State ◽

Heat And Mass Transport ◽

State Models

In this study numerical solutions are obtained using quasi steady state and unsteady state conditions to predict the reduction in concentrations of polluting hydrocarbons. Before their release to the atmosphere these gases undergo catalytic after-treatment in a converter, causing a decrease in their concentrations. Both homogenous as well as heterogeneous reactions are considered for hydrocarbons propylene and propane. Quasi steady and unsteady state models are developed to simulate heat and mass transfer between the exhaust gas and the catalyst surface, convective heat and mass transport, chemical reactions and the related heat release along with heat conduction in the substrate.

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Thermal Modeling of HRSG Transient Behavior in Combined Cycle Power Plants

Volume 4: Cycle Innovations; Electric Power; Industrial and Cogeneration; Manufacturing Materials and Metallurgy ◽

10.1115/gt2006-90718 ◽

2006 ◽

Author(s):

Sepehr Sanaye ◽

Moein Rezazadeh ◽

Jalaleddin Oladi ◽

Gholam Hossein Sadeghpoor ◽

Farid Bashiri ◽

...

Keyword(s):

Steady State ◽

Power Plants ◽

Cold Start ◽

Combined Cycle ◽

Operating Conditions ◽

Master Program ◽

Load Change ◽

Start Up ◽

Program Software ◽

Transient And Steady State

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.

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Nanocrystalline ZrO2 and Pt-doped ZrO2 catalysts for low-temperature CO oxidation

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.8.29 ◽

2017 ◽

Vol 8 ◽

pp. 264-271 ◽

Cited By ~ 23

Author(s):

Amit Singhania ◽

Shipra Mital Gupta

Keyword(s):

Co Oxidation ◽

Oxygen Vacancies ◽

Space Velocity ◽

Gravimetric Analysis ◽

X Ray Diffraction ◽

Solution Combustion ◽

Charge Imbalance ◽

Transmission Electron ◽

Co Conversion ◽

Low Temperature Co Oxidation

Zirconia (ZrO2) nanoparticles were synthesized by solution combustion using urea as an organic fuel. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), UV–vis and Fourier transform infrared (FTIR) measurements were performed in order to characterize the catalyst. The calculated crystallite size of ZrO2, calculated with the help of the Scherrer equation, was around 30.3 nm. The synthesized ZrO2 was scrutinized regarding its role as catalyst in the oxidation of carbon monoxide (CO). It showed 100% CO conversion at 240 °C, which is the highest conversion rate reported for ZrO2 in literature to date. It is found that through solution combustion, Pt2+ ions replace Zr4+ ions in the ZrO2 lattice and because of this, oxygen vacancies are formed due to charge imbalance and lattice distortion in ZrO2. 1% Pt was doped into ZrO2 and yielded excellent CO oxidation. The working temperature was lowered by 150 °C in comparison to pure ZrO2. Further, it is highly stable for the CO reaction (time-on-stream ≈ 40 h). This is because of a synergic effect between Pt and Zr components, which results in an increase of the oxygen mobility and oxygen vacancies and improves the activity and stability of the catalyst. The effects of gas hourly space velocity (GHSV) and initial CO concentration on the CO oxidation over Pt(1%)-ZrO2 were studied.

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Approximate analysis of the containment of contaminated sites prior to remediation

Water Science & Technology ◽

10.2166/wst.2000.0332 ◽

2000 ◽

Vol 42 (1-2) ◽

pp. 319-324 ◽

Cited By ~ 1

Author(s):

H. Rubin ◽

A. Rabideau

Keyword(s):

Steady State ◽

Peclet Number ◽

Dimensionless Parameter ◽

Contaminated Sites ◽

Unsteady State ◽

Péclet Number ◽

Vertical Barrier ◽

Time Period ◽

Barrier Performance ◽

Vertical Barriers

This study presents an approximate analytical model, which can be useful for the prediction and requirement of vertical barrier efficiencies. A previous study by the authors has indicated that a single dimensionless parameter determines the performance of a vertical barrier. This parameter is termed the barrier Peclet number. The evaluation of barrier performance concerns operation under steady state conditions, as well as estimates of unsteady state conditions and calculation of the time period requires arriving at steady state conditions. This study refers to high values of the barrier Peclet number. The modeling approach refers to the development of several types of boundary layers. Comparisons were made between simulation results of the present study and some analytical and numerical results. These comparisons indicate that the models developed in this study could be useful in the design and prediction of the performance of vertical barriers operating under conditions of high values of the barrier Peclet number.

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Investigation of Co–Fe–Al Catalysts for High-Calorific Synthetic Natural Gas Production: Pilot-Scale Synthesis of Catalysts

Catalysts ◽

10.3390/catal11010105 ◽

2021 ◽

Vol 11 (1) ◽

pp. 105

Author(s):

Tae Young Kim ◽

Seong Bin Jo ◽

Jin Hyeok Woo ◽

Jong Heon Lee ◽

Ragupathy Dhanusuraman ◽

...

Keyword(s):

Natural Gas ◽

Spinel Phase ◽

Space Velocity ◽

Pilot Scale ◽

Gas Production ◽

Laboratory Scale ◽

Optimum Conditions ◽

Synthetic Natural Gas ◽

Co Conversion ◽

Ft Ir

Co–Fe–Al catalysts prepared using coprecipitation at laboratory scale were investigated and extended to pilot scale for high-calorific synthetic natural gas. The Co–Fe–Al catalysts with different metal loadings were analyzed using BET, XRD, H2-TPR, and FT-IR. An increase in the metal loading of the Co–Fe–Al catalysts showed low spinel phase ratio, leading to an improvement in reducibility. Among the catalysts, 40CFAl catalyst prepared at laboratory scale afforded the highest C2–C4 hydrocarbon time yield, and this catalyst was successfully reproduced at the pilot scale. The pelletized catalyst prepared at pilot scale showed high CO conversion (87.6%), high light hydrocarbon selectivity (CH4 59.3% and C2–C4 18.8%), and low byproduct amounts (C5+: 4.1% and CO2: 17.8%) under optimum conditions (space velocity: 4000 mL/g/h, 350 °C, and 20 bar).

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Facile Preparation of Mesoporous MCM-48 Containing Silver Nanoparticles with Fly Ash as Raw Materials for CO Catalytic Oxidation

Micromachines ◽

10.3390/mi12070841 ◽

2021 ◽

Vol 12 (7) ◽

pp. 841

Author(s):

Dong Tian ◽

Yonghong Chen ◽

Xiaoyong Lu ◽

Yihan Ling ◽

Bin Lin

Keyword(s):

Silver Nanoparticles ◽

Fly Ash ◽

Co Oxidation ◽

Surface Composition ◽

Raw Materials ◽

Silica Source ◽

Co Conversion ◽

Co Catalytic Oxidation ◽

Adsorption Desorption

An environmentally friendly method was proposed to prepare mesoporous Mobil Composition of Matter No.48 (MCM-48) using fly ash as the silica source. Silver nanoparticles were infiltrated on MCM-48 facilely by an in situ post-reduction method and evaluated as an effective catalyst for CO oxidation. The as-prepared MCM-48 and Ag/MCM-48 nanoparticles were characterized by XRD, N2 adsorption/desorption, and TEM. Investigations by means of XPS for Ag/MCM-48 were performed in order to illuminate the surface composition of the samples. Studies revealed the strong influence of the loading of Ag nanoparticles on catalysts in the oxidation of CO. CO conversion values for Ag/MCM-48 of 10% and 100% were achieved at temperatures of 220 °C and 270 °C, respectively, indicating that the Ag-decorated MCM-48 catalyst is extremely active for CO oxidation.

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