Effect of Co and Mo Loading by Impregnation and Ion Exchange Methods on Morphological Properties of Zeolite Y Catalyst

Coal tar can be used as an alternative raw material for the production of liquid fuels, such as: gasoline and diesel through hydrogenation and cracking process. Hydrogenation and cracking process requires a catalyst which has metal components for hydrogenation reaction and acid components for cracking reaction. In this study, the Co/Zeolite Y and Co-Mo/Zeolite Y catalysts were prepared by impregnation and ion exchange methods. Characterizations of the catalysts were carried out by X-Ray Diffraction (XRD) and gravimetric acidity. The catalysts were tested for coal tar conversion to liquid fuel under various temperatures, amount of catalyst and hydrogen flow rates in a fixed bed flow reaction system. Liquid fuels products were analyzed by gas chromatography (GC). The XRD Spectra indicated that the addition of Co and Mo metals did not affect catalysts structure, however it alters the percentage of crystallinity. The addition of Co metal using impregnation method caused reduction in crystallinity, while the addition of Mo caused improvement of crystallinity. The Co-Mo/Zeolite Y catalyst with highest crystallinity was obtained by loading using ion exchange method. The addition of Co and Mo metals caused increasing acidity. However, the increasing composition of Co and Mo loaded on Zeolite Y catalyst decreased the yield of liquid fuels from coal tar. It can be concluded that the yields of liquid fuels and the composition of gasoline fractions from hydrocracking of coal tar were highly dependent on acidity of the catalyst. Copyright © 2016 BCREC GROUP. All rights reserved


Introduction
Due to its abundant reserve, coal has received major attention to replace petroleum as future primary energy source in Indonesia [1].Coal is a solid fossil fuel containing a variety of organic and inorganic components.Unfortunately, coal liquefaction has a negative effect to the environment due to the production of coal tar as by product.The liquefaction of 1 ton coal may produce 8-12 gallons of coal tar.Coal tar also contains aromatics, such as: benzene, toluene, phenol, and others that can be harmful to humans, fish, and wildlife [2].Therefore, efforts to increase the economic value of coal tar by processing it into more useful materials such as fuel are urgently required.
Coal tar is produced from coal gasification process, commonly in the form of carbon darkviscous liquid of hydrocarbons C7-C20 with molecular weight of 200-1200 [3].High molecular weight, viscosity and heteroatom compounds (S and N) have classified coal tar as a low quality fuel [4].Coal tar contains a mixture of aliphatic, aromatic, alicyclic and heterocyclic components [2].Coal tar can be used to produce liquid fuels, such as: gasoline and diesel oil, through the process of hydrocracking [5].With the aim to enhance the hydrocracking ability of the catalysts, more acid supports, such as: zeolite and TiO2, have been used [6][7][8][9][10][11]. Besides, the conventional cracking function of the acidic sites, the catalytic activities for hydrogenation unsaturated compounds and removal of heteroatoms were also improved with zeolite supports [12][13][14].
Zeolite is considered as a low cost good catalyst, because it has large pores, surfaces area and high acidity.In the petroleum processing industry, zeolite was used as an acid catalyst in cracking [15].The hydrocracking catalyst must have the ability to with hold from sulfur and nitrogen components contained in coal tar, so that the catalyst can be kept in good condition.Cobalt metal was selected for Zeolite Y catalyst modification due to its high selectivity and abil-ity to with hold the poison of sulfur and nitrogen components contained in coal tar.The incorporation of cobalt metal with zeolite Y and Co-Mo with zeolite Y can be done by method of impregnation or ion exchanges.Emelik et al. [16] and Tsitsihvli [17] have successfully conducted catalyst impregnation and ion exchange method for natural zeolite using Ni 2+ solution.The results showed that Ni 2+ ions were successfully incorporated into zeolite at concentration of 2.0 M and temperature of 400˚C.
In this study, Co-Mo based zeolite Y catalysts were used as a hydrocracking catalyst for coal tar and resulted in light hydrocarbon fraction as liquid fuel.The purposes of the research are to analyze the effect of Co and Mo loaded zeolite Y based catalysts on catalyst morphology prepared by impregnation and ion exchange over coal tar hydrocracking.

Materials
Coal tar was obtained from PT. Sango ceramics Indonesia.

Catalyst preparation by impregnation
Co-Mo/Zeolite Y catalyst was prepared by impregnation method [18] using the following steps: 0.59 gram Co(NO3)2.6H2Oand 0.5 gram (NH4)6Mo7O24.4H2Owas dissolved in 25 ml aquadest, and followed by addition of 5 grams of Zeolite Y.The mixture was stirred at 30 ˚C for 5 minutes and oven dried at 110˚C for 24 hour.The dried mass was finally calcined in a box furnace at temperature 550 ˚C for 3 hour.

Catalyst preparation by ion exchange
The catalysts were prepared using an aqueous solution of bimetal Co and Mo compounds loaded on zeolite Y by ion exchange methods.The preparation are as follows: Co(No)3.6H2Oand(NH4)6Mo7.4H2Odissolved in 25 mL aquadest with addition of 5 grams of zeolite Y, as tabulated on Table 1.The mixture was stirred at 30 ˚C for 5 h, followed by drying at 110 ˚C for 24 h.Finally, the solid were calcined in a box furnace at temperature of 550 ˚C for 3 h.

Characterization and testing catalyst
Crystallinity of the catalyst samples were analyzed by X-Ray Diffraction (XRD) and total acid amount were analyzed by gravimetric using pyridine and ammonia gasses.The catalyst were tested for coal tar conversion to liquid fuel with hydrocracking processes carried out under variable operating conditions of temperature and pressure in a fixed bed tube reactor with 1 inch ID.The activity test were operated using three variables, i.e. amount of catalyst, temperature reaction and flow rate of H2.The liquid yields were analyzed by gas Chromatography (GC).[19].The percentage of crystallinity of catalysts is calculated by using Equation 1 using data from X-Ray Diffraction [20].

Catalyst prepared by impregnation method
(1) The effect of cobalt loading of Zeolite Y on catalyst crystallinity was tabulated in Table 2. Table 2 showed that more cobalt added to Zeolite Y with the same amount of Mo, more the reduction in the percentage of crystallinity of catalyst.This is because the incorporated Co metal moved inside pores of the zeolite, and  hence lowering catalyst crystallinity.Table 3 shows the effect Mo loaded zeolite Y on catalyst crystallinity.It can be seen that more Mo is added to the catalyst with the same amount of Co, the percentage of crystallinity of the catalyst improved significantly.This may be due to many of Mo metal attached on surface of the catalyst, thus forming crystals and increase the percentage of crystallinity.
3.1.2.Characterization of the catalyst acidity using ammonia gas gravimetry Acidity analysis using gravimetric method employing ammonia gas was used to determine the acidity of a catalyst [21].Effect of addition of Co on acidity of the catalyst samples is tabulated in Table 4. Table 4 shows that the addition of Co on Zeolite Y catalyst at the same amount of Mo increases the catalyst acidity.This may be due to the addition of Co caused the absorption of ammonia gas is increased.
Table 5 is tabulated the effect of Mo loaded on the catalyst acidity.Table 5 showed that if the addition of Mo on the catalyst is increased with the same amount of Co, it causes increased acidity of the catalyst.This is likely due to the Mo metal increases ammonia gas adsorption.

Testing of catalyst
The reactions mechanism of coal tar hydrocracking into liquid fuel are illustrated in Figure 2. Yield of liquid fuel depends on the catalyst acidity.Results of the catalysts testing under different amount of cobalt and molybdenum are tabulated in Table 6.The reaction temperature was 350 ˚C and the catalyst amount of catalyst is 7 grams, i.e. 5 grams of catalyst which has been prepared (Co-Mo/Zeolite Y) and 2 grams of catalyst ZSM-5.Increasing of X1 (cobalt metal) to produce liquid fuel yield with range of 0.5-1.5% for X2 (molybdenum metal) to produce liquid fuel yield with range of 1-1.5%.The increase in composition of cobalt metal and molybdenum metal leads to increased acid

Bulletin of Chemical Reaction Engineering & Catalysis, 11(1), 2016, 78
Copyright © 2016, BCREC, ISSN 1978-2993 value, and hence the yield on liquid fuels was decreased.This is because the effect on the hydrogenation of coal tar cracking on the acid value of the catalyst.The catalyst performance test indicated that the yield of liquid fuels decreased as the acid value increased.

Catalyst characterization by X-Ray Diffraction (XRD)
Figure 3 indicates that X-ray spectra of Co-Mo/Zeolite Y catalyst has a similar pattern with Zeolite Y but in general show some differences in intensity at certain 2θ.The differences indicate the amount of loaded metals   3 show that Co and Mo loaded into Zeolite Y has crystallinity of 84.25%.The loading of metal on Zeolite Y caused reduction in percentage of crystallinity on the catalyst.This is because the metals loading on the catalyst samples cover the surface of catalyst pores, which finally altered.Characteristics of the zeolite crystal as indicated by decreasing the intensity may be due to partial loss of structural cations of zeolite.However, the peak intensity of Zeolite Y decreases still within the limits of tolerance.

Characterization of the catalyst acidity using gravimetric method
The catalyst acidity test was carried out using gravimetric method with pyridine gas adsorption.Aim of this method is to determine the amount of acid sites on the catalyst.The results of Co-Mo/Zeolite Y concentration is 4.22 mmol/gram pyridine.This result is higher than the amount of acidity of Zeolite Y, i.e. 3.09 mmol/gram pyridine.The increasing catalyst acidity caused the Mo metal loading into zeolites pore has 6 unpaired electrons in d orbitals than loading Co metal having 3 unpaired electrons in d orbital.The metals transition having full d orbitals are not effective as electron -pair acceptors of adsorbate.As contributor of Lewis acid sites is able to increase the acidity of catalyst [22].

Testing of catalyst
Testing of catalyst for hydrocracking process of coal tar using Co and Mo loaded Zeolie Y catalysts were conducted by 16 experimental runs (Table 7), which used the response surface methodology by 3 factorials 4 star points, and 4 center points.The products of hydrocracking coal tar were hydrocarbons of C6-C11 or gasoline ranges.The chromatogram shows that the retention time of the compounds ranges from 1.8-18.50similar to the standard gasoline C6-C11.
Table 7 indicated that the yield of liquid fuels using Co-Mo/Zeolite Y catalyst is higher (1.9%) than using Zeolite Y catalyst (1.0%).This is due to that the acidity of Co-Mo/Zeolite Y catalyst is higher (3.88) than Zeolite Y catalyst (3.58).According to Wega et al. [21] stated the catalyst performance test and indicated that the yield of liquid fuels increased as the acid value increased.

Catalyst characterization by X-Ray Diffraction (XRD)
The catalyst crystallinity of 0.59 g Co and 0.5 g Mo loaded Zeolite Y on catalyst morphology by impregnation and ion exchange methods from XRD analysis are 83% and 84%, respectively.Higher catalyst crystallinity can be achieved by ion exchange method rather than impregnation method.This is because reduction of surface area the metal loaded Co-Mo Zeolite Y indicates a strong interaction between the surface zeolite Y and Co and Mo [22] enabling good dispersion of the metals on the surface.

Characterization of the catalyst acidity using ammonia and pyridine gases gravimetric method
The acidity of catalyst using 0.59 g Co and 0.5 g Mo loaded Zeolite Y by impregnation method is higher than by ion exchange method.Comparing catalyst acidity using ammonia gas gravimetric of 0.59 Co -0.5 Mo/Zeolite Y catalyst using impregnation method obtained 9.19 mmol/gram, as well as by ion exchange was obtained of 4.22 mmol/gram.The amount of acid sites indicated by ammonia adsorption is greater than the vapor of pyridine because it has stronger base than pyridine.The size of molecules contained ammonia relative smaller than pyridine so it is easier adsorp to the surface of the pore than pyridine only adsorb to the pore surface [23].

Coal tar hydrocracking to liquid fuel
The coal tar hydrocracking reaction was done using 5 grams of catalyst which was prepared (Co-Mo/Zeolite Y) and 2 grams of catalyst ZSM-5 at 350 o C with a flow rate of 5 mL/min.The yield of liquid fuels using 0.59 g Co and 0.5 g Mo loaded zeolite Y catalyst using impregnation method was 1.8%, while its gasoline composition was 1.75%.The 0.59Co-0.5Mo/ZeoliteY catalyst of ion exchange method for hydrocracking of coal tar carried by using independent variable amount of catalyst, reaction temperature and hydrogen flow rate obtained optimum yield of 1.42% and gasoline composition 7.27%.
A comparison of performance testing of catalyst obtained by impregnation method and ion exchange methods showed that the yields of liquid fuels using impregnation method is higher than the ion exchange method.However, catalyst obtained by ion exchange method results in higher composition of gasoline fractions.This indicates that a process of reaction formation via carbocation, where each ion carbonium production will induce other compounds to form new carbonium ion with a smaller number of atoms, with the addition of metallic Co and Mo can improve high activity in the hydrocracking of coal tar.It is evident from the high results of the composition of the product.In addition to the greater composition of metals, cobalt and molybdenum metals also affect the process of hydrogenation of coal tar cracking in the power value of the acid catalyst.Lin et al. [24] showed that the activation energy of a reaction will decrease drastically with increasing acid strength of a catalyst, especially in the process that has a lot of reaction.

Conclusions
Loading of Co and Mo on Zeolite Y catalyst prepared by using impregnation and ion exchange method did not change the structure of catalysts.The percentage of catalyst crystallinity for catalyst prepared by ion exchange method was high, while acidity of the catalyst was high for the catalyst prepared by using impregnation.The yields of liquid fuels using impregnation method was greater than using ion exchange method, however composition of fractions gasoline greater if using ion exchange method.These results can be concluded that the yields of liquid fuels and the composition of fraction gasoline from hydrocracking of coal tar depend on the acidity of catalyst.If the acidity of catalyst was high, the yield of liquid fuels was increased, however the composition of gasoline fraction was decreased.

3. 1 . 1 .
Catalyst characterization by X-Ray Diffraction (XRD) Based on XRD diffractogram (Figure 1) all samples have the same peaks, especially between 0-35 o .The appeared 2θ of 35 o peak indicates the presence of Co and Mo metals in the surface of the catalyst.

Figure 1 .
Figure 1.XRD Diffractogram of all catalyst samples obtained from impregnation method 2θ ( o )

Figure 2 .
Figure 2. The mechanism reactions of hydrocracking coal tar into liquid fuel

Figure 3 .
Figure 3.The XRD Spectra of the samples of zeolite Y and Co-Mo/zeolite Y

Table 1 .
Catalyst of Co-Mo/Zeolite Y prepared by ion exchange method With similarities peak of both Zeolite Y and Co and Mo impregnated Zeolite Y catalysts, they indicate no change in crystal form in all samples of Zeolite Y catalyst.Base on some literatures, cobalt nitrate hexahydrate peaks should appear on 2θ of 15.10 o ; 15.61 o ; 27.06 o ; 28.09 o ; 30.55 o

Table 3 .
Effect of Mo on zeolite crystallinity

Table 4 .
Effect of Co on catalyst acidity

Table 5 .
Effect of metal Mo on catalyst acidity

Table 2 .
Effect of Co on zeolite crystallinity

Table 6 .
Testing hydrocracking coal tar when using catalyst by impregnation method The addition of Co and Mo metals to Zeolite Y causes the formation of amorphous structure on the Co-Mo/Zeolite Y.The XRD spectra of the Zeolite Y and Co-Mo/Zeolite Y catalysts as depicted in Figure

Table 7 .
Testing hydrocracking coal tar using catalyst by ion exchange method