The Catalyst Review (December 2016) - 12

EXPERIMENTAL
The catalytic results in Figure 2 illustrate the effects of both zeolite structure and composition on the ETP reaction. A notable
difference (95 vs 16%) in the initial ethene conversion was found over H-SSZ-13 and H-SAPO-34. In addition, the ethene conversion
over H-SSZ-13 rapidly decreases with TOS so that it becomes almost the same as the conversion over H-SAPO-34.
A combination of GC-MS and DFT calculation results reveals that the superior ETP performance of this large-pore zeolite comes
from its unique cylindrical cages in which ethene can be effectively converted to isopropyl-naphthalene-based hydrocarbon species
which, in turn, plays a central role as reaction centers in propene formation. Apart from the relatively lower coke forming tendency
compared to H-SSZ-13 with small 8-ring windows, the ETP stability of H-UZM-35 can be further improved by mild dealumination.
Source: Lee K, Cha SH, and Hong SB. (2016). ACS Catal. 6: 3870-3874.

Nitrogen-Based Fuels: A Power-to-Fuel-to-Power Analysis...
In the face of increasing greenhouse gas emissions, efforts to develop carbon-neutral energy technologies are now focusing the use
of hydrogen as the ultimate clean fuel source. However, the ability to safely store and distribute hydrogen on a global basis are nontrivial concerns. Herein, the authors compare carbon- and nitrogen-based fuels on an energy basis as chemical hydrogen-storage
media for stationary power generation by providing metrics by which these alternatives can be critically compared.
They begin by defining the so-called
Figure 1. Material and energy streams of the PFP system. Process boundaries are marked by
power-to-fuel-to-power (PFP) index as
dashed lines.
the ratio of the available output power
from a fuel's combustion to the energy
required for its production (by water
splitting, air separation, and synthesis)
and distribution. Thus, the PFPatm index
represents the relationship between
the combustion efficiency (the fraction
of a fuel's heating value that is converted
to power), and the atmosphere is the
feedstock for both N2 and CO2. Seven
synthetic fuels were evaluated:
methane, methanol, dimethyl ether
Table 1. PFPatm indices of the seven assessed alternative fuels.
(DME), ammonia, aqueous ammonium
hydroxide urea (AHU), aqueous
ammonium hydroxide ammonium
nitrate (AAN), and aqueous urea
ammonium nitrate (UAN). The material
streams entering the system boundaries
are water and air, while the material
outlet streams are oxygen from water
splitting, the byproducts of air separation,
water from the fuel's synthesis, and
the combustion effluent (Figure 1). The
calculated PFPatm indices vary in the
range of 12%-35% as noted in Table 1.
Ammonia has the lowest required energy
for feedstock separation, even when
compared to carbon-based fuels in the
case of flue-gas-derived CO2. The normalized energy required for water splitting is highest for the UAN-based fuels. The normalized
energies required for fuel synthesis are particularly low for the simple molecules, methane and ammonia.
The authors go on to demonstrate that a nitrogen economy, wherein renewable hydrogen is chemically stored on abundant nitrogen
in the form of a nontoxic and safe nitrogen-based alternative fuel, is energetically feasible. In addition, the novel nitrogen-based fuels
which were investigated, especially aqueous UAN, are comparable on an energy-return basis to existing carbon-based fuels. Source:
Dana AG, Elishav O, André Bardow A, et al. (2016). Angew. Chem. Int. Ed. 55: 8798-8805.

The Catalyst Review

December 2016

The Catalyst Review (December 2016)

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