Catalysts and processes for tunable base-grown multiwalled carbon nanotubes

A method of decomposing a lower hydrocarbon, the method consisting of the steps of:

• heating a catalyst bed to a temperature of about 500° C. to about 1000° C. at a heating rate of about 1° C. min-1 to about 20° C. min-1;
• wherein the catalyst bed comprises a metal-supported catalyst;
• wherein the metal-supported composition comprises a 3d transition metal selected from Ni, Fe, Co, Mn, Cr, and Mo and a support material selected from a silica, an alumina, a zeolite, titanium dioxide, or a mixture thereof;
• wherein the 3d transition metal is present in an amount from about 5 wt % to about 70 wt % based on the total weight of the 3d transition metal and the support material;
• and
• wherein the support material is present in an amount from about 95 wt % to about 30 wt % based on the total weight of the 3d transition metal and the support material,
• wherein the metal-supported catalyst is positioned within a reactor;
• wherein the reactor has a fixed-bed or a moving bed flow reactor configuration;
• wherein the reactor comprises an inlet end and an outlet end for gas flow;
• providing a flow of a reactant gas through to the inlet end at a reactant gas flow rate equivalent to a space velocity of about 5,000 h-1 to about 60,000 h-1;
• wherein the flow of the reactant gas is in contact with the catalyst bed;
• and
• wherein the reactant gas comprises a lower hydrocarbon and an inert gas;
• collecting an outflow gas at the outlet end;
• wherein the outflow gas comprises hydrogen;
• regenerating the catalyst consisting of terminating the flow of reactant gas and providing a regeneration gas to the catalyst bed;
• wherein the regeneration gas is in contact with the catalyst bed for a contact period from about 5 minutes to about 240 minutes;
• wherein the temperature of the catalyst bed is from about 250° C. to about 750° C.;
• and
• wherein the regeneration gas comprises oxygen;
• and repeating the heating, the providing a flow of the reactant gas, the collecting the outflow gas, and the regenerating the catalyst for 1-10 cycles.