Hydrogen Utilization in Chemical Processes - Hydrogen Generation, Storage, and Utilization - page 185

theory calculation shows that hydrogen most stable in the positive charge
state in p -type GaN, explaining the experimentally observed passivation of
acceptors [30]. Likewise, H − passivates donors in n -type GaN. In both cases,
hydrogen always counteracts the prevailing conductivity and cannot act as a
dopant in GaN [31].
There are some other cases in which hydrogen can also behave exclusively
as donor or acceptor. For example, H + is the only stable charge state in ZnO,
based on density-function theory calculation [32]. In this case, hydrogen will
always give up its electron, thus increasing the concentration of free electrons
and enhancing the electrical conductivity of ZnO. This is consistent with
previously reported experimental results [28, 33, 34].
10.7 SUMMARY
In this chapter, we have briefly reviewed some examples of important appli-
cations of hydrogen gas beyond combustion and fuel cells. In the petroleum
industry, hydrogen is mainly used for hydrocracking and hydroprocessing of
crude oil, which produce large amounts of fossil fuels for commercial use.
Hydrogen gas is also an essential material in the production of ammonia and
nitrogen fertilizers through the Haber process, as well as hydrogenation of
unsaturated hydrocarbons in chemical industry and organic synthesis. More-
over, hydrogen has been extensively used as reducing reagent for metal ore
reduction. Lastly, hydrogen also can serve as a kind of lifting gas, a refriger-
ant for cooling superconductors and a dopant for semiconductors to modify
their electronic properties. It is clear that hydrogen gas is essential for a
number of extremely important chemical processes. Hydrogen sustainability
is therefore critical for material supplies and economy growth. It is highly
desired to develop environmentally friendly and sustainable methods for
hydrogen production.
REFERENCES
1. Scherzer, J., Gruia, A.J. Hydrocracking Science and Technology , CRC Press, New York,
1996.
2. Ward, J.W. Hydrocracking processes and catalysts. Fuel Process Technology , 1993 , 35 (1-
2), 55-85.
3. Weitkamp, J. Catalytic hydrocracking-mechanisms and versatility of the process. Chem-
CatChem , 2012 , 4 (3), 292-306.
4. Belokopytov, Y. Reaction mechanism in hydrogenolysis of chlorobenzene over nickel-
chromium catalyst. Theoretical and Experimental Chemistry , 1998 , 34 (5), 280-282.