The Effect of Zr loading on the Performance of Honeycomb Monolithic catalyst for the Removal of NO , CO and Hydrocarbon from Exhaust Gas

Catalytic monolith reactors have n umerous applications in indu strial processes a nd as technical devices, so t he fo cus is set sp ecially on automotive catalytic converters. In present work the experimental and theoretical investigation has been carried out to study the performance of monolith reactor on the oxidation and r eduction of exhaust gas (NO, C O, HC, O 2 and H 2 O) which emitted from gasoline generator. Commercial ceramic monolith catalyst and catalyst loaded on the commercial with Zr were used in the present work. A laboratory u nit was c onstructed for this purpose where a versatile stainless steel reactor of 0.02 m inside diameter and 0.2 m height was used. The catalytic performance of the c atalysts was studied in the following operating conditions: gas hourly space v elocity in the range 17. 69 – 44. 23s -1 , reaction temperature in the range 373 – 673 K, bed length in the range 0.075 – 0.15 m and at atmospheric pressure and constant air / fu el ratio (14.6). The results show that the conversion of NO, CO, HC, O 2 a nd H 2 O are slightly c hanged with the bed length, . The c onversion o f e xhaust gas re actant enhances in presence o f water (wet condition) rather t han in the absence of water (dry condition) and increases with the increasing reaction temperature a nd decreases with increasing gas space velocity. Commercial catalyst loaded with 0.4% Zr gives t he higher performance for all components reaction


Introduction
Automobile exhaust gases are a major source of manmade emissions.Many improvements were made by engine modifications.However, 1975 U.S Federal and California limits could not met by engine modifications alone and the catalytic converter was shown to be the best forward.Considerable research into catalytic system was taken by both industry and academics.Catalysts using base metals such as nickel, copper, cobalt and iron seemed initially to be attractive on the basis of cost.However, these catalysts were adversely affected by sulfur and residual traces of lead in the fuel, and catalysts eventually chosen were based on the platinumgroup metals.For a few years, the emission limit could be reached by oxidation of carbon monoxide and hydrocarbon emitted by the engine (Andrzej 1998), as in equations ( 1) and (2):- The most common catalyst called conventional oxidation catalyst (two ways catalyst) was based on platinum and palladium on the alumina support (Cybulski 1994).However, as legislation tightened further, it became necessary to control the NO x emission.This brought two further requirements: closer around the stoichiometric air/fuel ratio, and the addition of a further catalytic metallic component, Rhodium, to the catalyst formulation to enable the NO x to be selectivitely reduced to nitrogen as in equation ( 3) and ( 4) (Johnson 1996): Monolith catalyst research since 1987 has focused on reactor design, increasing efficiency and the search for more suitable catalyst.Thus the complete oxidation of CO and HC and reduction of NO can be found over either noble metal (Pt, Pd and Rh) or other metal oxide (Ba and La ) (Kendal, 2003;Ismagilov, 1998).The investigation beyond 1997s on the addition of CeO and ZrO 2 to the monolithic catalyst shows that these components as stabilizers of the alumina surface area enhance the performance of the monolithic catalyst (Horiuchi et al., 1999;Tadashi et al., 2002;Vidal et al., 2001 andPriscila et al., 2005).During the last years, extensive efforts were made to develop new formulations, reporting on the specific role of platinum, palladium and rhodium in single and multiple compositions on the total conversion under real conditions, and studied the aging resistance of the catalyst under oxidizing, reducing environments.The Effect of Zr loading on the Performance of Honeycomb Monolithic catalyst for the of NO, Removal CO and Hydrocarbon from Exhaust Gas Furthermore, the Platinum / Rhodium threeway catalyst converter is an essential device in controlling the three regulated pollutant emissions (CO, NO x and HC) (Granger et al., 2002;Peter et al., 2004).Also, a new generally three way catalyst using ceriumzirconium mixed oxide was under intensive research (Di Monte et al., 2002, Fabiono et al., 2007).

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The aims of the present work is to prepare one type of metal catalyst on the commercial three way catalyst by impregnation method , study the catalyst performance in wide rang of temperatures , gas space velocity and bed length at atmospheric pressure and stochoimetry air/ fuel ratio .

-Feed Gases
Average emission gases produced from commercial gasoline generator (Single piston Astra 2.5 kv) are used as feedstock in this investigation.-The Procedure: The flow rate of reactants (gas emitted from generator) was adjusted to the desired value for each particular experiment.The mixture of reactants was entered the preheating zone and then passed the catalyst bed after it was heated to desired temperatures.After 20 minutes, when steady state condition was obtained the samples were taken from the outlet condenser to be analyzed by gas chromatography.
The abovementioned procedure was used for wet condition study.During the dry condition, cyclone was placed before the reactor entrance to remove the humidity from the emission gases, therefore samples were taken from the outlet of cyclone analyzed by gas chromatography to insure that the gases were dried.

-Analysis System:
Reactants and products were analyzed by a gas chromatography (GC) (SHIMADZU -14A) equipped with a thermal conductivity detector (TCD).The apparatus consists of two stainless steel columns, the length of each column is 2 m and of 0.317 cm internal diameter.The first column is open tube coated with porapaq N and the second with porapaq Q.The porapaq particle dimension is of 80-100 mesh.The temperature program for the column is shown in Table ( 6).
The injection system is located at the head of the column, where the sample under consideration was injected inside column.A syringe of 0.25 ml total capacity was used for this purpose.The sample analysis and the corresponding signals were recorded and integrated by a digital integrator (SHIMADZU -CR 4A).The analysis was done in Ibin Sina Company.

-Results and Discussion:
Sixty column experiments were carried out to study the effect of various initial conditions on the performance of monolithic reactor on the oxidation and reduction of exhaust gases (NO, CO, and HC). -

Effect of Operating Variable on Monolith Performance
-The Effect of Bed Length Twelve experiments, as shown in Table (5 ).Table (7),and Figures (3 to 6) show the effect of bed length on conversion of the exhaust gas reactants for NO reduction and C 3 H 6 and CO oxidation.From these figures, it can be noticed that the conversion slightly changes with the bed length, so there is no appreciable external mass transfer limitation for both NO reduction and CO and C 3 H 6 oxidation.This observation is noted also by (Chalrabarti andSharma 1993, George et al., 2004)

-Estimation of Reaction Kinetic Parameters
The kinetic rate prediction is necessary for the reactor and monolith catalyst model simulation.The overall catalytic reactions that are important for controlling exhaust condition are given by questions 5 to 8 below.The kinetic reaction rate is considered to follow simple power law.Differential method analysis is used to estimate the reaction rate for small variation in the conversion or for shallow small reactor (Levenspiel, 1999).
The results of the analysis of the parameters estimation are outlined in Table (8) From Table ( 8), the apparent activation energy values are in the range of (17-56 KJ/mol), this indicates that the internal diffusion severely limits the reaction as mentioned also by Farrauto, (1997). - Pro trial version www.pdffactory.comEng.& Tech.Journal ,Vol.27,No.10, 2009 ), were carried out at different bed lengths (0.075 -0.15 m) and different temperatures (373 -673 K) at constant space velocity (23.61 sec - 1

Table (
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& Tech. Journal ,Vol.27, No.10, 2009
The Effect of Zr loading on the Performance of Honeycomb Monolithic catalyst for the of NO, Removal CO and Hydrocarbon from Exhaust Gas

Table ( 2) Chemical and physical properties of monolith catalyst
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Table ( 3) The amount of reagents used for preparation of 0.4 % Zr catalysts
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Journal ,Vol. 27, No.10, 2009
The Effect of Zr loading on the Performance of Honeycomb Monolithic catalyst for the Removal of NO, CO and Hydrocarbon from Exhaust Gas 1925

Table ( 5) Operating condition of experiments
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Table (8) Apparent activation energy values and reaction order for commercial cata
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