Table 3. Overview of Recent Studies Conducted on Various Metal-Impregnated Carbonaceous Catalysts for the CDM Reaction^a.

no.	catalyst	preparation method	metal loading (wt. ratio %)	SBET (m2/g)	operating parameters	CH4 conversion (mol %)	carbon produced	ref
1	Ni/AC (coal)	impregnation	6.7		0.2 g of catalyst	13% (t = 0)	web-like filamentous carbon (tube size = 50 nm)	(98)
					T = 1023 K	5% (t = 2h)
					50 mL/min CH4
2	Ni/AC (coconut shells)	impregnation	30	565.12 (before)		29% (t = 0)	highly degenerated soot and carbon fibers	(99)
				179.0 (after)		75% (t = 4h)
3	Ni/RC (shenhua coal)	in situ preparation with carbon	10	589	T = 850 °C	15% (t = 0)	some filamentous carbon formed	(100)
						25% (t = 4 h)
4	Ni/AC (coconut shells)	impregnation	30	1185 (before)	VHSV= 1.62 L/h·gcatT = 850 °C	10% (t = 15 min)	carbon nanofibers (diameter 100–200 nm and length 5–8 μm) surrounded by sooty carbon	(101)
				565.12 (after)		30% (t = 4h)
5	Ni/CB (petroleum base)	impregnation	30	120 (before)		5% (t = 15 min)
				65.1(after)		20% (t = 4 h)
6	Ni–Co/AC (saimengte coal)	in situ during activation	20 (Ni)	326		75% (t = 0)	spherical encapsulated carbon with some amount of fibers	(102)
			20 (Co)			34% (t = 5 h)
7	Ni–Fe/AC (saimengte coal)		20 (Ni)	68		20% (t = 0)	relatively higher amount of carbon fibers than spherical
			20 (Fe)			75% (t = 5h)
8	Ni/CC (blue coke)	selective steam gasification	6.87	265 (before)	VHSV = 12 L/h·gcat	50% (t = 0)	fibrous carbon	(103)
				41 (after)	T = 850 °C.	70% (t = 10h)
9	Ni/C (pine saw dust)	selective steam gasification (t = 30 min)	57.31	16.48		70% (t = 0)	fibrous carbon	(104)
						90% (t = 6 h)
10	Ni–K/CC	selective steam gasification with residual K2CO3 (used as catalyst)			VHSV= 12 L/h·gcatT = 850 °C	60% (t = 0)	encapsulated carbon	(105)
						25% (t = 2h)
11	Ni/CC	selective steam gasification without residual K2CO3	17.66	128 (before)		55% (t = 0)	carbon fibers
				25 (after)		90% (t = 10h)
12	Ni–sucrose/C	selective steam gasification	35.87	26.4	VHSV = 24 L/h·gcat	≈90% (t = 10h)	filamentous carbon (fibers + some encapsulation structures)	(106)
					T = 850 °C
13	Ni/3DOMC	steam-assisted crystallization	47.4	884	0.336 g of catalyst	10% (t = 0)	graphitic carbon	(107)
					VHSV = 12.5 L/h·gcat	50% (t = 10h)
					T = 850 °C.	48% (t = 4h)
14	Ni–Cu/CNT	polyol reduction method	78(Ni):22(Cu)		0.05 g of catalyst	55% (t = 0)	branched CNFs	(108)
					Total flow rate = 20 mL/min	50% (t = 14 h)
					T = 850 °C.	20% (t = 26h)
15	Fe–Al/AC (coconut shell)	impregnation	22.16(Fe)	492	0.1 g catalyst,	37% (t = 0)	encapsulated carbon	(109)
					VHSV = 15 L/h·gcat	17% (t = 2.5h)
					T = 850 °C.
16	Fe/AC (Shenmu coal)	in situ during carbonization-activation	23	762	VHSV = 15 L/h·gcat	25% (t = 0)	carbon fibers along with encapsulating carbon structures	(110)
					T = 850 °C.	14% (t = 6 h)
17	Pd/AC	impregnation	10	751.56 (before)	VHSV = 1.62 L/h·gcat	37.5% (t = 0)	carbon nanofibers (diameter 40–250 nm; 9 μm length)	(111)
				245.17 (after)	T = 1123 K	52.5% (t = 4h)
18	Pt/AC (ash wood biomass)	impregnation	20.5	919	0.05 g of catalyst	11.3% (t = 0)	thin layer carbon deposition	(112)
					0.6 L/h methane	1% (t = 1.5 h)
					T = 850 °C
19	Pd/AC (ash wood biomass)	impregnation	19.42	864			chaotically arranged filaments of different lengths (20–200 nm)
20	Ca/AC	impregnation	15	1838	0.2 g of catalyst	21% (t = 0)	hyaline carbon surface deposits with some carbon fibers.	(113)
					VHSV = 15 L/h·gcat	8% (t = 6 h)
					T = 850 °C.
21	Ru/AC	impregnation	3.16	690	WHSV = 0.1 h–1	20% (t = 60h)	CNT	(114)
					T = 800 °C.

^aAbbreviations are as follows: S_BET = BET surface area, T = temperature, VHSV = vapor hour space velocity, t = time, AC = activated carbon, CC = coal char, 3DOMC= three-dimensional ordered mesoporous carbon, CNT = carbon nanotube, and CB = carbon black