**1. Introduction**

Due to the elevated level of population growth, energy consumption has risen over the recent decade [1]. This increase in energy demand over the years has changed the energy scenario through manufacturing [2]. Furthermore, even with the current low oil price, the world's energy demand is anticipated to continue to rise in the future according to the international energy agency's new policy situation [3], from 13.2% in 2011 up to 17.6% in 2035 as shown **Figure 1**.

Currently, dependence on fossil fuels such as petroleum, gas and coal to satisfy energy demand has caused environmental issues owing to anthropogenic greenhouse gas generation. Methane (CH4) and carbon dioxide (CO2) are the most

**Figure 1.**

*Primary energy demand in Mtoe (million tonnes of oil equivalent) (a) 2011, (b) 2035 "new policies scenario" and (c) 2035 "450 scenario" (adapted from Ref. [3]).*

abundant greenhouse gasses and have lately contributed significantly to climate change issues [4]. While the level of methane in the environment is smaller than that of carbon dioxide [5], it is surprising that around 20% of worldwide warming occurs is caused by it [6]. Conventionally, there are two main sources of methane emissions including nature occurring activities and anthropogenic activities. Examples of the first source are termites, grasslands, coal beds, lakes, wetlands and forest fires, while examples from the second source are landfills, oil and gas treatment, wastewater treatment plants, coal mining, rice production, livestock and agricultural activities [7]. According to the US Environmental Protection Agency [8], methane manufacturing from landfill sites accounts for almost one-third of all methane produced in the United States alone, where landfill gas consists of 40–45% methane and 55–60% carbon dioxide by quantity by volume [9]. Notwithstanding, the reality that methane is a significant element of natural gas, a big quantity of natural gas is burned globally owing to technological constraints and the high price of carrying this valuable gas from its reservoirs, which are often far from industrial fields and the prospective market [10]. These actions have wasted an important source of hydrocarbons and contributed to global warming by releasing greenhouse gases into the atmosphere [11]. Carbon dioxide capture and storage (CCS) has been implemented globally to decrease carbon dioxide emissions due to pressure to combat global climate change and guarantee viable power sources [12]. In addition, renewable energy is required instantly to replace oil resources to decrease the heavy dependence on crude oil and its unwanted impacts on the atmosphere [13].

In the last few years, the resources of renewable energy, particularly, biogas, have gained massive attention around the world as a substitute for traditional fossil fuels [14]. In Southeast Asia, palm oil biomass is considered one of the most plentiful renewable resources and has enormous potential for the sustainable production of chemical substances and fuels. Liquid waste, known as palm oil mill effluent (POME) generated along with crude palm oil production, is one of Southeast Asia's environmental problem due to its high pollution characteristics. Therefore, digestion, an aerobic treatment, is widely adopted in the oil palm industries as a reliable and

*Catalysts for the Simultaneous Production of Syngas and Carbon Nanofilaments… DOI: http://dx.doi.org/10.5772/intechopen.101320*

effective treatment for POME. The biogas generated during POME's anaerobic decomposition is not restored for use, but can be dissipated into the atmosphere [15]. The biogas produced contains two greenhouse gases: methane (60–70%) and carbon dioxide (30–40%) with traces of hydrogen sulfide which can be utilized after purification for heat generation, electricity production, bio-methane production and of synthesis gas (referred to as syngas, mixture of H2 and CO) [16]. In fact, POME could become a significant source for biogas production due to its high organic content [17]. According to the World Meteorological Organization [18], methane and carbon dioxide levels were reported at 1845 ppm (parts per million) and 400.1 ppm (parts per million) respectively in 2015. Methane levels in the environment have been revealed to be below carbon dioxide levels, but have caused about 20% of worldwide warming [19]. Methane production was estimated at 6875 million metric tons which equals the total amount of carbon dioxide from all anthropogenic sources in 2010 [20]. Methane is frequently considered an important natural gas component with small amounts of other hydrocarbons such as ethane, propane and butane containing inert substances such as molecular oxygen (O2) and carbon dioxide [21]. When monitoring the negative impact of methane and carbon dioxide, it is paramount to reduce their concentrations so that to avoid the high concentration of the greenhouse gases that lead to negative environmental conditions and increased temperature.

A great deal of extensive studies has been conducted to discover efficient methods of converting methane and carbon dioxide into precious products and thus reducing their elevated atmospheric quantity. Because of its comparatively low price and stability relative to other methods, converting carbon dioxide and methane into syngas is one of the most prevalent technologies [22]. It is one of the most important processes to convert hydrocarbons in the chemical industries to produce syngas [23]. In many distinct applications, such as Fischer-Tropsch (F-T) petroleum synthesis and the manufacturing of methanol and other precious fluid fuels and chemicals, syngas can be regarded as a construction block [24].

Recently, there have been many attempts that have prompted interest in producing alternative fuels by using renewable and environmentally friendly sources of energy, one of the few alternative sources is biogas. Even so, it is not entirely greenhouse gas-free; it does not, however, lead to global warming. Biogas is an appealing alternative for converting fuel to transport and generate electricity [25]. The vital route that will be of benefit to the power generation industry is the direct conversion of biogas, composed of methane and carbon dioxide to hydrocarbons under catalytic decomposition processes.

The use of catalysts in the catalytic reaction is essential in growing syngas manufacturing, as they assist to alter and enhance the reaction rate without consumption in the process [26]. Catalysts operate by offering an alternative mechanism that decreases energy activation, which implies the system needs less energy to achieve the state of transition. While catalytic reaction needs elevated temperatures to operate due to its heat-absorbing nature, the existence of catalysts can significantly decrease the reaction temperature [27].

Recently, there have been many attempts to use monometallic catalysts such as Ni, Co, Fe and Cu in the catalytic process because they are cheap and have a strong magnetization ability [28, 29]. Furthermore, bimetallic such as Ni-Co, Ni-Fe, and Ni-Cu have become very attractive to researchers due to their properties and the diversity of applications when compared with their individual mono-metal counterparts. The incorporation of nickel into Co, Fe, and Cu metals decreases the use of expensive noble metals [30]. Bimetallic catalysts success is thought to be due to the synergy of their parent metals they consist of two separate metals that display elevated dispersion and active sites. Moreover, the physical and chemical properties of the bimetallic catalysts are enhanced due to the formation of the solid solution

[31]. For example, Pudukudy et al. [32] and Pinilla et al. [33] revealed a greater carbon output from a bimetallic catalyst compared to a monometallic catalyst.
