Method of producing hydrogen gas using nanocomposite catalyst
A method of producing hydrogen gas comprising hydrolyzing sodium borohydride (NaBH 4 ) with water at a temperature of from about 20° C. to about 75° C. in the presence of a particulate crystalline nanocomposite catalyst, where the ratio by weight of NaBH 4 to the particulate crystalline nanocomposite catalyst is from about 1:1 to about 5:1. The particulate crystalline nanocomposite catalyst comprises a calcium hydrogen phosphate (CaHPO 4 ) crystalline phase, a calcium silicate hydroxide [Ca 6 Si 6 O 17 (OH) 2 ] crystalline phase, a silicon oxide (SiO 2 ) crystalline phase, graphitic carbon nitride (C 3 N 4 ) crystalline phase, wherein at least a fraction of the graphitic-C 3 N 4 is in the form of mesoporous nanosheets.
1 . A method of producing hydrogen gas, comprising:
hydrolyzing sodium borohydride (NaBH 4 ) with water at a temperature of from about 20 to about 75° C. in the presence of a particulate crystalline nanocomposite catalyst,
wherein the ratio by weight of sodium borohydride to the particulate crystalline nanocomposite catalyst is from about 1:1 to about 5:1,
wherein the particulate crystalline nanocomposite catalyst comprises:
a CaHPO 4 crystalline phase;
a Ca 6 Si 6 O 17 (OH) 2 crystalline phase;
a SiO 2 crystalline phase; and,
a graphitic-C 3 N 4 crystalline phase,
wherein at least a fraction of the graphitic-C 3 N 4 is in the form of mesoporous nanosheets.
2 . The method according to claim 1 , wherein based on the weight of the particulate crystalline nanocomposite:
CaHPO 4 is present in an total amount of from about 20 to about 40 wt. %;
Ca 6 Si 6 O 17 (OH) 2 is present in an amount of about 20 to about 30 wt. %;
SiO 2 is present in an amount of from about 1 to about 10 wt. %; and,
C 3 N 4 is present in an amount of about 20 to about 30 wt. %.
3 . The method according to claim 1 , wherein the particulate crystalline nanocomposite comprises acicular particles of Ca 6 Si 6 O 17 (OH) 2 having a median length of from about 20 to about 80 nm, as determined by Transmission Electron Microscopy.
4 . The method according to claim 1 , wherein the particulate crystalline nanocomposite comprises aggregates of the mesoporous nanosheets of graphitic-C 3 N 4 with substantially spherical particles of SiO 2 and CaHPO 4 .
5 . The method according to claim 1 , wherein the particulate crystalline nanocomposite comprises aggregates of:
the mesoporous nanosheets of graphitic-C 3 N 4 ; and,
substantially spherical particles of SiO 2 and CaHPO 4 having a median particle size of from about 5 to about 30 nm, as determined by Transmission Electron Microscopy.
6 . The method according to claim 1 , wherein at least about 50 wt. % of the graphitic-C 3 N 4 is in the form of mesoporous nanosheets.
7 . The method according to claim 1 , wherein at least about 80 wt. % of the graphitic-C 3 N 4 is in the form of mesoporous nanosheets.
8 . The method according to claim 1 , wherein the particulate crystalline nanocomposite has an average pore diameter of from about 10 to about 25 nm, as determined by Barrett-Joyner-Halenda (BJH) desorption analysis.
9 . The method according to claim 1 , wherein the particulate crystalline nanocomposite has an average pore diameter of from about 15 to about 25 nm, as determined by Barrett-Joyner-Halenda (BJH) desorption analysis.
10 . The method according to claim 1 , wherein the particulate crystalline nanocomposite has a pore volume of from about 0.1 to about 0.4 cm 3 /g, as determined by Barrett-Joyner-Halenda (BJH) desorption analysis.
11 . The method according to claim 1 , wherein the particulate crystalline nanocomposite has a pore volume of from about 0.2 to about 0.3 cm 3 /g, as determined by Barrett-Joyner-Halenda (BJH) desorption analysis.
12 . The method according to claim 1 , wherein the particulate crystalline nanocomposite has a hysteresis loop of Type H3 (IUPAC Classification), as determined by N 2 adsorption-desorption analysis at 77K.
13 . The method according to claim 1 further comprising preparing the particulate crystalline nanocomposite by:
forming a solution of a calcium salt and an alkali metal silicate in a solvent comprising water and a C 1 -C 4 alkanol;
heating the solution at a temperature of from about 150 to about 250° C. to form a dry product of CaSiO 3 ;
forming graphitic-C 3 N 4 by heating urea in a closed vessel at a temperature of from about 500 to about 700° C.;
dispersing the CaSiO 3 , graphitic-C 3 N 4 and P 2 O 5 in a polar protic solvent and heating the dispersion at a temperature of from about 150 to about 250° C. at a pressure of from about 2 to about 8 Bar; and,
separating the solid crystalline nanocomposite from the heated dispersion.
14 . The method according to claim 1 , wherein the ratio by weight of sodium borohydride to the particulate crystalline nanocomposite catalyst is from about 1:1 to about 3:1.
15 . The method according to claim 1 , wherein sodium borohydride is hydrolyzed with water at a temperature of from about 25 to about 70° C.
16 . The method according to claim 1 , wherein sodium borohydride is hydrolyzed with water at a temperature of from about 35 to about 60° C.
17 . The method according to claim 1 having a hydrogen generation rate of from about 100 to about 1500 mL min −1 g −1 based on the weight of the sodium borohydride (NaBH 4 ).
18 . The method according to claim 1 having a hydrogen generation rate of from about 200 to about 1500 mL min −1 g −1 based on the weight of the sodium borohydride (NaBH 4 ).