5. Conclusion

With the steam reaction having more advantage of generating extra hydrogen via water gas shift reaction, it is unexpected to record lower hydrogen composition compared to nitrogen environment. However, it is easy to perceive that the unaccounted hydrogen for the steam experiments have been consumed during hydrogenation, hydrodesulfurization and de-coking as reported earlier. On the contrary, one would expect that the high composition of hydrogen reported in the experiment without steam would increase the upgrading, lower coke formation or improve olefin saturation. Nevertheless, it has been reported that the proton formed via water gas shift reaction has higher hydrogenating reactivity than others [13].

Another observation in Table 2 is the high volume of methane recorded in the reaction without steam. In the presence of water and a suitable catalyst, methane undergoes steam-methane reforming (SMR) to produce syngas according to

In a bid to further explore the resourcefulness of syngas in hydrocracking of heavy crude oil and bitumen, hydrogenation could progress either through the forward water gas shift reaction (Eq. 3) or reverse water gas shift reaction (Eq. 25).

hydrodesulfurization of dibenzothiophene using NiMo/Al2O3 catalysts at 673 K and 30 MPa [61]. Four different mixtures; hydrogen-water, carbon monoxide-water, carbon dioxide-hydrogen-water, and HCOOH-water were used as hydrogen sources, and conversion were obtained in the order; carbon monoxide-water, carbon dioxide-hydrogen-water, HCOOH-water and hydrogen-water. It would be observed that the carbon monoxide-water and carbon dioxide-hydrogen-water combinations are the forward and reverse water gas shift reactions respectively. Product analysis of the carbon dioxide-hydrogen-water mixture revealed trace amount of carbon monoxide a product of reverse water gas shift reaction (Eq. 25). Basically, there are two mechanisms postulated for the water gas shift reaction; the regenerative mechanism and the associative mechanism. In the regenerative mechanism, the redox reaction on the surface of the catalysts is responsible for the hydrogen production [66]. It is proposed that the catalysts surface is oxidized by water to produce hydrogen followed by reduction of the surface to convert carbon

For the associative mechanism, an adsorption-desorption model was proposed which involves intermediate and eventual desorption to carbon dioxide and hydro-

Syngas is acclaimed to be the energy of the future [7]. Hydrogen on the other hand has found application as a direct fuel in hydrogen internal combustion engine,

A comprehensive research structure was used to demonstrate this in

monoxide to carbon dioxide as seen in Eqs. (26) and (27).

CH<sup>4</sup> þ H2O ! 3H<sup>2</sup> þ CO (24)

CO<sup>2</sup> þ H<sup>2</sup> ! CO þ H2O (25)

H2O þ red ! H<sup>2</sup> þ ox (26) CO þ ox ! CO<sup>2</sup> þ red (27)

CO þ H2O ! ð Þ! intermediate CO<sup>2</sup> þ H<sup>2</sup> (28)

Eq. (24).

Sustainable Alternative Syngas Fuel

gen (see Eq. 28).

4. Sustainability

40

Water gas shift reaction is an important step in the production of syngas. Interestingly, the sustainability of syngas span across the raw materials, process and application in fuel production as alternative to current and future energy demands. Worthy of note is its application in upgrading over 8 trillion barrels heavy crude oil and bitumen resources via water gas shift reaction to produce low molecular weight hydrocarbon separated into gases, liquefied petroleum gas (LPG), gasoline, naphtha, kerosene, diesel, gas oil, lubricating oil, greases and so on in a conventional refinery. For this purpose, hydrogen is produced in-situ from syngas with a suitable oxide catalysts and water from dehydrated or non-dehydrated crude. Upgrading via syngas gave lower viscosity and higher saturates. The process is also economically viable and environmentally friendly because of the absence of hydrogen gas in the feedstock and lower hydrogen sulfide in the gaseous product stream respectively. Although, heavy crude oil and bitumen are non-renewable fossil fuels, their abundant reserves and method of in-situ hydrogen generation during upgrading qualifies them as future alternative fuel and sustainable resource respectively.

## Conflict of interest

The authors declare no conflict of interest.

Sustainable Alternative Syngas Fuel
