Preparation and Characterization of Metal Carbide Zeolite Composite Catalysts

The object of present work is to synthesize metal carbide zeolite composite catalysts and discusses their characteristics. Metal carbide with zeolite composite was prepared in the present research. Molybdenum carbide was used as a metal carbide which was prepared by solid-state method with Ammonium molybdate tetrahydrate and commercial activated carbon as raw materials. Ion exchanged method was used to add platinum to the HY zeolite. Modified Y zeolite was prepared by using ion exchanged method by mixing the HY zeolite with Cerium nitrate. After prepared Mo2C, PtHY zeolite, and CeY a formation process take place in order to form two catalysts the first one is Mo 2 C/PtHY-Zeolite, while the second one is Mo 2 C/CePtY zeolite. Tests such as X-Ray Diffraction, Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR), and Thermal Gravimetric Analysis (TGA) were performed on both catalysts and the results were as follows for the molybdenum carbide the surface area was 1072 m 2 /g


Introduction:
Platinum (Pt), while being costly, is a necessary catalyst material for many reactions with industrial uses because of its activity and stability [1].One such method is continuous catalytic reforming, which has been used in the petroleum industry for over seven decades and uses platinum as an active metal component.In fact, this expensive metal accounts for more than 90% of the total cost of the catalyst.So, examining other metals and materials have activity and stability that can compared with this noble metal, became an urgent need.Carbon is incorporated into the interstitial sites of transition metals to generate transition metal carbides (TMC) (add reference).These carbide samples show unusually blended ionic crystals, covalent solids, and transition metal characteristics.
These substances have high melting points and electrical characteristics comparable to ionic solids, are tougher than covalent solids, and are thermally stable same as transition metals [2].The transition metals' lattice is enlarged and their metal-metal bond distance is increased by the addition of carbon.Theoretical estimates indicating, in TMCs, charge transfer from metal to carbon cause constriction of the d-band and movement of the density of states for the Fermi level related to its parent metal are supported by experimental findings [3].These TMC materials have characteristics like to those of the Pt group metals because their electronic states are close to the Fermi level [4].
Due to these special qualities, experts from all over the world are very interested in carbide materials.Under the tested experimental settings, these non-noble materials are used as replacements for expensive metals like Platinum, on a personal level with the Platinum-based catalyst, in the reactions of the oxygen reduction process, isomerization, hydro-deoxygenation, and hydrogenation [5][6][7].As was already mentioned, TMC materials like tungsten and molybdenum carbides have been effectively used as catalysts for the important metal-based isomerization and dehydrogenation processes in naphtha reforming.Yet, unlike the noble metal Pt which did not work un supported, transition metal carbide can be employed unsupported, which may explain why the catalyst behavior is not similar to that of Pt.Even though, (TMC) are sharing the same electrical structure as platinum, to be active for the reactions [8].The majority of research on carbide catalysts is motivated by Levy and Boudart's significant work [9].Who hypothesized that out of the eight group metals, except for Cu and Au, Pt, Ir, and Au can catalyze the isomerization of 2,2dimethypropane to 2-methylbutane.In order to serve as the counter electrode in dye-sensitized solar cells, Wu et al. [10] produced composites of MoC embedded in order nano mesoporous carbon materials.The characterization revealed that MoC electrodes had a larger positive potential than Pt electrodes.The MoC-based electrode, in contrast side, produced an 8.34% energy conversion efficiency, which is greater than Platinum (7.98%), according to the photocurrent-voltage experiment.Their findings suggested that molybdenum carbide may be used in place of the precious Platinum counter electrode.According to Chen et al. [11], MoC supported by Al2O3 was used in the hydrazine decomposition reaction.The findings of the experiment demonstrated that Mo2C/-Al2O3 catalysts had an outstanding catalytic performance for the decomposition of hydrazine.
Additionally, the catalytic activity was equivalent to that of noble metal.Ir.Ji et al. [12] researched supported molybdenum carbide catalysts for catalyzing the conversion of cellulose to polyols, particularly EG (ethylene glycol).According to their findings, the conversion of cellulose by Pt/AC (active carbon) was modest, at 66%, while the AC-supported MoC catalyst resulted in better conversion of the cellulose (85%).Those findings are also suggested that Molybdenum Carbide might serve as an affordable replacement catalyst for Pt noble metal catalysts [13].
High selectivity is another benefit of using molybdenum carbide as a catalyst.Molybdenum carbide frequently exhibits distinctive catalytic pathways, resulting in desired product selectivity, as a result of the electron redistribution once carbon is introduced into the molybdenum bulk.For instance, Han et al. [14] revealed that the molybdenum carbide (Mo2C/AC) supported nano-sized active carbon may effectively catalyze the conversion of renewable oils in the hydrocarbon mixtures that resemble diesel.The selectivity of olefins on Mo2C/AC catalyst when the stearic acid was the substrate was significantly greater (85.8%) than that of the Pd nanoparticle catalyst (77.4%).
Molybdenum carbide was also explored by Qin et al. [15] as a catalyst for the hydrodeoxygenation of vegetable oils.and discovered that the Mo2C/CNF (carbon nanofiber) catalyst resulted in good selectivity and activity, and the catalytic performance exhibited no discernible decrease after being recycled five times table (1) will show the basic advantage and disadvantages of molybdenum carbide.
The object of present work is to synthesize metal carbide zeolite composite catalysts and discusses their characteristics.

Experimental work 2.1 Materials
Table (1) shows all the chemicals was used in this study, and Table (2) illustrate the advantages and disadvantages of the molybdenum carbide.

Preparation process of Molybdenum carbide
Solid-state synthesis was used to create molybdenum carbide supported on activated carbon.In a standard procedure, activated carbon was added to the metal salt solution and agitated by a heating and magnetic stirrer (the stirrer has a thermometer that can adjust the temperature and keep it constant at a certain degree) for two hours at 130 degrees Celsius, followed by solvent evaporation and drying in a 150 C oven for 4 hours Prepared Solid-state reaction carbide materials uniformly combined the carbon and metal precursor were heated at three different temperatures of 800 ,900 & 1000 degrees Celsius at a ramp rate of 4.5 C/h under nitrogen flow and stay at those temperatures for two hours.The catalyst was cooled to room temperature after the reaction.Figure (1) shows the steps and tubular furnace that used to calcinate the substance.0.43gm of hexachloro platinic acid was added to 175ml of distal water at room temperature, then 70 g of HY-Zeolite was added to the solution and stirred for 30min without exposing it to heat and leaving the solution to sedimentation until the next day.After one day the solution was filtered, washed, and then entered into a drier to evaporate all water from it.The white powder reduced from this procedure was calcinated at 260℃ for 3hr.The percentage of Platin is 0.25% to HY-Zeolite.
Figure (2) shows the steps of the procedure.The powder of zeolite HY was modified by ion exchange via nitrate solutions of cerium cation Ce(NO3)3 with a certain concentration.The sample is exchanged at 80 °C for 8 hours in accordance with the previously mentioned ratio of 50 g Zeolite HY to 600 mL nitrate solution, after which they were all filtered, washed, dried at 120 °C for 8 hours, and then calcined at 600 °C for 5 hours to produce a Ce modified Zeolite Y.
 Loaded Pt on the prepared CeY modified zeolite 0.25% is the percentage of the platin in this catalyst.0.14 g of hexachloroplatinic acid dissolved in distilled water inside the separated funnel then Add the powder after calcination to a flask and vacuum the air out of it and then start adding the solution slowly as in Figure (3) then mix it well and leave it to the next day.After that the substance was washed, filtered, and dried then it entered the furnace at 600℃ for 6hr [16].Figure (3) shows the steps of the procedure.o Catalyst 2 Mo2C / CePtY zeolite Catalyst.showing a high level of crystallization for the band of 2 θ from 20° to 75° for the produced substance on the XRD analysis.By comparing the sharp peak at 2θ equal to 42 with Hodala et.all.[1] which has the same peak at 2θ equal to 40.Using Scherer's equation, the crystal size L was determined as follows.

𝐵(2𝜃) = 𝐾 𝛾 𝐿 𝑐𝑜𝑠𝜃
Where: B: is the FWHM of the peak at 2 .K: is the Scherrer's constant, which can range from 0.6 to 2.08 depending on the crystal form; here we consider it [1].
Scherrer's equation applied to X-ray diffraction data yields an average crystal size for Mo2C of 18.65 nm.

Fig. (4): XRD of the molybdenum carbide 2. BET surface area and Bore volume analysis
The prepared molybdenum carbide had a surface area of 1029.787m 2 /g and which is better than Hodala et al. [1]Who synthesized molybdenum carbide at 800 ℃ and got a surface area of 835m 2 /g [1].The pore volume of the prepared molybdenum carbide was 0.514 cm 3 /g.a large surface area is due to the raw materials that used to prepare molybdenum carbide.This means it has huge macroporous particles and little mesoporous particles, which means more spaces among particles.

Fourier transform infrared spectroscopy FTIR
The chemistry of the surface of the catalyst was considered by the infrared method as shown in Figure (5).the region between 3465-3889 cm -1 reveals the OH stretching on the catalyst, the bands in the range of 2373.22-2344.89cm -1 indicate the presence of H2O, so long as the band at about 1558 cm -1 assigned to (COOH, CH2, COO) at the surface of the catalyst.The bands in 1077 cm -1   reveal to C-O bond.This is the same result was obtained by Yu J. et al. [17]

BET surface area and Bore volume analysis
The synthesized sample Mo2C.Pt/HY-Zeolite has an overall BET surface area of 724.55 m 2 /g.larger surface area means a larger pore volume which makes the cataltyst more active when using it for its purpose.

A thermogravimetric analysis (TGA)
Thermogravimetric analysis (TGA) is an analytical method that analyzes the weight change that happens when sample is heated at a constant rate in order to test a material's thermal stability and the percentage of volatile components.Figure (7) shows the TGA for the prepared sample.The test shows a weight loss of 10.21% from the sample at a temperature range of 130-900 ℃.From the point at 130 C to the point at 400 C the mass loss is high around 9% of the substance this is because the water evaporation as a result of rise the temperature.

Fourier transform infrared spectroscopy FTIR
The FT-IR spectra of the produced Mo2C/PtHY Zeolite is represented in Figure (8).The IR band 2344 cm -1 is caused by the stretching vibration of OH molecules.then, the IR band at 1633 cm -1 is caused by the molecules' bending vibration.The band at 1057 cm -1 is due to the C_C bond's symmetric stretching vibration.The detected band at 795 cm -1 is due to the bond's bending vibration.

Conclusion
In this study, two catalysts were synthesized, Mo2C/PtHY and Mo2C/CePtY.Both substances were completely tested to know their properties as shown earlier.
After synthesizing molybdenum carbide at three different temperatures the best characteristics were obtained at 900℃ so it was used to prepare the two catalysts.
For the Mo2C/PtHY zeolite and Mo2C/CePtY, the BET surface area was 724.55 m 2 /g and 734.55 m 2 /g respectively, the large surface area of these two catalysts is due to the large surface area of the molybdenum carbide that used to produce these catalysts.The Mo2C/PtHY zeolite's XRD pattern revealed that it had the same crystal phase structure as Zeolite Y.The Scherrer equation suggests that the average crystal size is 20.77 nm, while the crystal size of Mo2C/CePtY is 40.43nm.A thermogravimetric analysis (TGA) for the Mo2C/PtHY shows that the weight loss from the sample from 130-900 C is 10.21%, while for Mo2C/CePtY is 4.64%.

Fig. ( 3 )
Fig. (3): Preparation of Pt/Ce/HY-Zeolite: A. ion exchange, B. Washing and filtering C. Add the Pt to the powder