Preparation And Catalytic Properties Of TiC,WC Matrix Porous Carbide

In this paper,Ni₃C-TiC,WC-TiC and SiC-WC composite was prepared by solid state sintering method in reduction atmosphere at 1560℃,phase exchange,crystal structure, oxidation resistance behavior,thermal expansion coefficient,mechanics performance,pore size distribution and microstructures were tested by X--ray diffraction(XRD),differential thermal analysis(DTA),thermal expansion device(TED),mechanics pressure machine, mercury intrusion porousimetry(MIP) and scanning electron microscope(SEM) instruments, the catalytic properties and catalytic mechanism of different composite carbide were discussed with the result of gas chromatography(GC) and gas chromatography-mass spectrometry(GC-MS).Result indicated that:In the Ni added porous composite TiC composite,Ni metal volatilized at high temperature,bonding the TiC matrix particles and transferred into Ni₃C in reduction atmosphere;the radius of composite carbide particle was between 2μm and 10μm with "mushroom cloud" shape,pores uniform distributed,1～5μm;Oxidation resistance increased from 675K to 820K with 10wt%Ni added.Porous WC-TiC composite was synthesized with different WC precursor tungsten oxide and ammonium paratungstate.As tungsten oxide was precursor,the diameter of prepared WC was 1～5μm.Connected pores with wide pore size distribution,0.3～5μm,and low surface area, 2.976m²/g,were formed for the decomposition of ammonium bicarbonate.When oxide was replaced by APT,the final WC uniform distributed with the radius of 50～200nm,the pores were bimodal distributed,200～800nm and 2～5μm,as the synergistic effect of APT and ammonium bicarbonate,the surface area increased to 4.082 m²/g.In the SiC-WC composite,as the percentage of Si increases from 2 wt%to 14wt%in batches,the thermal expansion coefficients are from 4.11×10^-6/K to 4.76×10^-6/K,it got the lowest point 4.11×10^-6/K when Si was 8wt%,the oxidation peak increased from 600K to 800K and their flexural strength decreased gradually,from 120MPa to 80MPa;The pore size distributions were unimodal(400nm,200～1000nm) and bimodal(700nm and 10μm, 400～1000nm and 5～20μm) without and with NH₄HCO₃ as a pore generating agent respectively. Porous nickel-titanium carbide composite was excellent catalyst for alcohol dehydration, the selectivity of ethylene was 98.41%at 380℃;the maximum alcohol velocity changed from 8ml/min to 200ml/min as temperature increased from 360℃to 500℃;among different concentration alcohol,75～99%,the conversion rate of reached maximum 98.4%at the alcohol concentration 95%,the selectivity increased gradually at the velocity of 50ml/min in 400℃.The selectivity of propylene first increased and then decreased as the temperature rises, it got the peak point 99.7%at 450℃;flow velocity of propanol did not had profound impact on selectivity when the flow velocity below 200ml/min,above 99%,but the selectivity decreased as the flow velocity surpassed 200ml/min.High surface area WC was novel catalyst for alkane isomerization.Tungsten carbide prepared by tungsten oxide had low surface area and bad catalytic properties,the selectivity of isopentane and pentane conversion rate at 350℃was 5.68%and 16.21%,respectively.The WC used APT as precursor with relative high surface area had high selectivity and conversion rate,12.91%and 48.44%at 350℃.The reaction was exothermic first order reaction;the calculated activation energy was 62.98kJ/mol with the reaction rate of different temperature.