The phrase "act duly" is correct and usable in written English.
It can be used in contexts where one is expected to perform their duties or responsibilities in a proper or appropriate manner.
Example: "As a member of the committee, I will act duly to ensure that all decisions are made fairly and transparently."
Alternatives: "perform appropriately" or "act properly".
The party's senators performed a remarkable volte-face and, last week, the Zadroga Act duly passed.
The Republican-led House of Representatives, led by Boehner, told Democrats, "Either you postpone the Affordable Care Act (duly passed by Congress, upheld by the Supreme Court and, in essence, ratified again by the electorate in the last presidential election) or we will shut down the country".
"Tidings of glorious face and lovely bloom," he wrote, "which stir and goad the regions turgid now with seed abundant; so that, as it were with all the matter acted duly out, they pour the billows of a potent stream and stain their garment".
"Steve Kember was brought in to perform the miracle act and duly delivered – ably assisted by Dougie Freedman, who played like a man possessed in those two games.
SEX -- Being half-naked all the time, Mathayus and Cassandra are more or less obliged to have sex at some point, which they do finally, but the act is duly obfuscated.
The government stopped conducting public executions in the early 20th century for much the same reason that it will use lethal injections rather than more brutal technologies to kill Timothy McVeigh -- to reinforce the distinction between a lynching and a soberly considered act of duly authorized justice.
Act 1 was duly released then, with sales funding Act 2 to follow later this year.
The act, ratified by duly elected representatives of the American people, signed into law by our (now twice-elected) president, and upheld by the Supreme Court, is now the law of the land.
The Light Dues Act 1852 was duly enacted by the Governor-General of India in Council on 30 January 1852.
According to Vidal, Boyd duly acted this as a love scene.
Why not join them?" His Bratz chair duly acts as an iPod speaker.
